MariaDB MaxScale Configuration Guide

MariaDB MaxScale Configuration Guide


This document describes how to configure MariaDB MaxScale and presents some possible usage scenarios. MariaDB MaxScale is designed with flexibility in mind, and consists of an event processing core with various support functions and plugin modules that tailor the behavior of the program.



Word Description
connection routing Connection routing is a method of handling requests in which MariaDB MaxScale will accept connections from a client and route data on that connection to a single database using a single connection. Connection based routing will not examine individual requests on a connection and it will not move that connection once it is established.
statement routing Statement routing is a method of handling requests in which each request within a connection will be handled individually. Requests may be sent to one or more servers and connections may be dynamically added or removed from the session.
module A module is a separate code entity that may be loaded dynamically into MariaDB MaxScale to increase the available functionality. Modules are implemented as run-time loadable shared objects.
connection failover When a connection currently being used between MariaDB MaxScale and the database server fails a replacement will be automatically created to another server by MariaDB MaxScale without client intervention
backend database A term used to refer to a database that sits behind MariaDB MaxScale and is accessed by applications via MariaDB MaxScale.
REST API HTTP administrative interface



A server represents an individual database server to which a client can be connected via MariaDB MaxScale. The status of a server varies during the lifetime of the server and typically the status is updated by some monitor. However, it is also possible to update the status of a server manually.

Status Description
Running The server is running.
Master The server is the primary.
Slave The server is a replica.
Draining The server is being drained. Existing connections can continue to be used, but no new connections will be created to the server. Typically this status bit is turned on manually using maxctrl, but a monitor may also turn it on.
Drained The server has been drained. The server was being drained and now the number of connections to the server has dropped to 0.
Auth Error The monitor cannot login and query the server due to insufficient privileges.
Maintenance The server is under maintenance. Typically this status bit is turned on manually using maxctrl, but it will also be turned on for a server that for some reason is blocking connections from MaxScale. When a server is in maintenace mode, no connections will be created to it and existing connections will be closed.
Slave of External Master The server is a replica of a primary that is not being monitored.
Master Stickiness The server is monitored by a galeramon with disable_master_failback=true. See disable_master_failback for more information.

For more information on how to manually set these states via MaxCtrl, read the Administration Tutorial.


A monitor module is capable of monitoring the state of a particular kind of cluster and making that state available to the routers of MaxScale.

Examples of monitor modules are mariadbmon that is capable of monitoring a regular primary-replica cluster and in addition of performing both switchover and failover, galeramon that is capable of monitoring a Galera cluster, and csmon that is capable of monitoring a Columnstore cluster.

Monitor modules have sections of their own in the MaxScale configuration file.


A filter module resides in front of routers in the request processing chain of MaxScale. That is, a filter will see a request before it reaches the router and before a response is sent back to the client. This allows filters to reject, handle, alter or log information about a request.

Examples of filters cache that provides query caching according to rules, regexfilter that can rewrite requests according to regular expressions, and qlafilter that logs information about requests.

Filters have sections of their own in the MaxScale configuration file that are referred to from services.


A router module is capable of routing requests to backend servers according to the characteristics of a request and/or the algorithm the router implements. Examples of routers are readconnroute that provides connection routing, that is, the server is chosen according to specified rules when the session is created and all requests are subsequently routed to that server, and readwritesplit that provides statement routing, that is, each individual request is routed to the most appropriate server.

Routers do not have sections of their own in the MaxScale configuration file, but are referred to from services.


A service abstracts a set of databases and makes them appear as a single one to the client. Depending on what router (e.g. readconnroute or readwritesplit) the service uses, the servers are used in some particular way. If the service uses filters, then all requests will be pre-processed in some way before they reach the router.

Services have sections of their own in the MaxScale configuration file.


A listener defines a port MaxScale listens on. Connection requests arriving on that port will be forwarded to the service the listener is associated with. A listener may be associated with a single service, but several listeners may be associated with the same service.

Listeners have sections of their own in the MaxScale configuration file.


An include section defines common parameters used in other configuration sections.


The administation of MaxScale can be divided in two parts:

  • Writing the MaxScale configuration file, which is described in the following section.
  • Performing runtime modifications using MaxCtrl

For detailed information about MaxCtrl please refer to the specific documentation referred to above. In the following it will only be explained how MaxCtrl relate to each other, as far as user credentials go.

Note: By default all runtime configuration changes are saved on disk and loaded on startup. Refer to the Dynamic Configuration section for more details on how it works and how to disable it.

MaxCtrl can connect using TCP/IP sockets. When connecting with MaxCtrl using TCP/IP sockets, the user and password must be provided and are checked against a separate user credentials database. By default, that database contains the user admin whose password is mariadb.

Note that if MaxCtrl is invoked without explicitly providing a user and password then it will by default use admin and mariadb. That means that when the default user is removed, the credentials must always be provided.

Administration audit file

The REST API calls to MaxScale can be logged by enabling admin_audit.

For more detail see the admin audit configuration values admin_audit, admin_audit_file and admin_audit_exclude_methods below and Administration Tutorial.

Static Configuration Parameters

The following list of global configuration parameters can NOT be changed at runtime and can only be defined in a configuration file:

  • admin_auth
  • admin_enabled
  • admin_gui
  • admin_host
  • admin_pam_readonly_service
  • admin_pam_readwrite_service
  • admin_port
  • admin_secure_gui
  • admin_ssl_ca
  • admin_ssl_version
  • admin_jwt_algorithm
  • admin_jwt_key
  • admin_jwt_issuer
  • auto_tune
  • cachedir
  • connector_plugindir
  • datadir
  • debug
  • execdir
  • language
  • libdir
  • load_persisted_configs
  • persist_runtime_changes
  • local_address
  • log_augmentation
  • log_warn_super_user
  • logdir
  • module_configdir
  • persistdir
  • piddir
  • query_retries
  • secretsdir
  • sharedir
  • sql_mode
  • substitute_variables
  • threads_max

All other parameters that relate to objects can be altered at runtime or can be changed by destroying and recreating the object in question.


MaxScale by default reads configuration from the file /etc/maxscale.cnf. If the command line argument --configdir=<path> is given, maxscale.cnf is searched for in \<path> instead. If the argument --config=<file> is given, configuration is read from the file \<file>.

MaxScale also looks for a directory with the same name as the configuration file, followed by ".d" (for example /etc/maxscale.cnf.d). If found, MaxScale recursively reads all files with the ".cnf" suffix in the directory hierarchy. Other files are ignored.

After loading normal configuration files, MaxScale reads runtime-generated configuration files, if any, from the persisted configuration files directory.

Different configuration sections can be arranged with little restrictions. Global path settings such as logdir, piddir and datadir are only read from the main configuration file. Other global settings are also best left in the main file to ensure they are read before other configuration sections are parsed.

The configuration file format used is INI, similar to the MariaDB Server. The files contain sections and each section can contain multiple key-value pairs.

Comments are defined by prefixing a row with a hash (#). Trailing comments are not supported.

# This is a comment before a parameter

A parameter can be defined on multiple lines as shown below. A value spread over multiple lines is simply concatenated. The additional lines of the value definition need to have at least one whitespace character in the beginning.



Section names may not contain whitespace and must not start with the characters @@.

As the object names are used to form URLs in the MaxScale REST API, they must be safe for use in URLs. This means that only alphanumeric characters (i.e. a-z A-Z and 0-9) and the special characters _.~- can be used.

Dynamic Configuration

By default all changes done at runtime via the MaxScale GUI, MaxCtrl or the REST API will be saved on disk, inside the persistdir directory. The changes done at runtime will override the configuration found in the static configuration files for that particular object.

This means that if an object that is found in /etc/maxscale.cnf is modified at runtime, all future changes to it must also be done at runtime. Any modifications done to /etc/maxscale.cnf after a runtime change has been made are ignored for that object.

To prevent the saving of runtime changes and to make all runtime changes volatile, add persist_runtime_changes=false and load_persisted_configs=false under the [maxscale] section. This will make MaxScale behave like the MariaDB server does: any changes done with SET GLOBAL statements are lost if the process is restarted.

Special Parameter Types


Boolean type parameters interpret the values true, yes, on and 1 as true values and false, no, off and 0 as false values. Starting with MaxScale 23.02, the REST API also accepts the same boolean values for boolean type parameters.


Where specifically noted, a number denoting a size can be suffixed by a subset of the IEC binary prefixes or the SI prefixes. In the former case the number will be interpreted as a certain multiple of 1024 and in the latter case as a certain multiple of 1000. The supported IEC binary suffixes are Ki, Mi, Gi and Ti and the supported SI suffixes are k, M, G and T. In both cases, the matching is case insensitive.

For instance, the following entries


are equivalent, as are the following



A number denoting a duration can be suffixed by one of the case-insensitive suffixes h, m or min, s and ms, for specifying durations in hours, minutes, seconds and milliseconds, respectively.

For instance, the following entries


are equivalent.

Note that if an explicit unit is not specified, then it is specific to the configuration parameter whether the duration is interpreted as seconds or milliseconds.

Not providing an explicit unit has been deprecated in MaxScale 2.4.

Regular Expressions

Many modules have settings which accept a regular expression. In most cases, these settings are named either match or exclude, and are used to filter users or queries. MaxScale uses the PCRE2-library for matching regular expressions.

When writing a regular expression (regex) type parameter to a MaxScale configuration file, the pattern string should be enclosed in slashes e.g. ^select -> match=/^select/. This clarifies where the pattern begins and ends, even if it includes whitespace. Without slashes the configuration loader trims the pattern from the ends. The slashes are removed before compiling the pattern. For backwards compatibility, the slashes are not yet mandatory. Omitting them is, however, deprecated and will be rejected in a future release of MaxScale. Currently, binlogfilter, ccrfilter, qlafilter, tee and avrorouter accept parameters in this type of regular expression form. Some other modules may not handle the slashes yet correctly.

PCRE2 supports a complicated regular expression syntax. MaxScale typically uses regular expressions simply, only checking whether the pattern and subject match at some point. For example, using the QLAFilter and setting match=/SELECT/ causes the filter to accept any query with the text "SELECT" somewhere within. To force the pattern to only match at the beginning of the query, set match=/^SELECT/. To only match the end, set match=/SELECT$/.

Modules which accept regular expression parameters also often accept options which affect how the patterns are compiled. Typically, this setting is called options and accepts values such as ignorecase, case and extended.

  • ignorecase: Causes the regular expression matcher to ignore letter case, and is often on by default. When enabled, /SELECT/ would match both SELECT and select.

  • extended: Ignores whitespace and # comments in the pattern. Note that this is not the same as the extended regular expression syntax that for example grep -E uses.

  • case: Turns on case-sensitive matching. This means that /SELECT/ will not match select.

These settings can also be defined in the pattern itself, so they can be used even in modules without pattern compilation settings. The pattern settings are (?i) for ignorecase and (?x) for extended. See the PCRE2 syntax documentation for more information.

Standard regular expression settings for filters

Many filters use the settings match, exclude and options. Since these settings are used in a similar way across these filters, the settings are explained here. The documentation of the filters link here and describe any exceptions to this generalized explanation.

These settings typically limit the queries the filter module acts on. match and exclude define PCRE2 regular expression patterns while options affects how both of the patterns are compiled. options works as explained above, accepting the values ignorecase, case and extended, with ignorecase being the default.

The queries are matched as they arrive to the filter on their way to a routing module. If match is defined, the filter only acts on queries matching that pattern. If match is not defined, all queries are considered to match.

If exclude is defined, the filter only acts on queries not matching that pattern. If exclude is not defined, nothing is excluded.

If both are defined, the query needs to match match but not match exclude.

Even if a filter does not act on a query, the query is not lost. The query is simply passed on to the next module in the processing chain as if the filter was not there.


Enumeration type parameters have a pre-defined set of accepted values. For types declared as enum, only one value is accepted. For enum_mask types, multiple values can be defined by separating them with commas. All enumeration values in MaxScale are case-sensitive.

For example the router_options parameter in the readconnroute router is a mask type enumeration:


Path Lists

A pathlist type parameter expects one or more filesystem paths separated by colons. The value must not include space between the separators.

Here is an example path list parameter that points to /tmp/something.log and /var/log/maxscale/maxscale.log:


Global Settings

The global settings, in a section named [MaxScale], allow various parameters that affect MariaDB MaxScale as a whole to be tuned. This section must be defined in the root configuration file which by default is /etc/maxscale.cnf.


  • Type: string list
  • Values: all or list of auto tunable parameters, separated by ,
  • Default: No
  • Mandatory: No
  • Dynamic: No

An auto tunable parameter is a parameter whose value can be derived from a particular server variable. With this parameter it can be specified whether all or a specific set of parameters should automatically be set.

The current auto tunable parameters are:

MaxScale Parameter Server Variable Dependency
connection_keepalive 80% of the smallest wait_timeout value of the servers used by the service
wait_timeout The smallest wait_timeout value of the servers used by the service

The values of the server variables are collected by monitors, which means that if the servers of a service are not monitored by a monitor, then the parameters of that service will not be auto tuned.

Note that even if auto_tune is set to all, the auto tunable parameters can still be set in the configuration file and modified with maxctrl. However, the specified value will be overwritten at the next auto tuning round, but only if the servers of the service are monitored by a monitor.


  • Type: positive integer or auto
  • Default: auto
  • Dynamic: Yes

This parameter controls the number of worker threads that are routing client traffic. The default is auto which uses as many threads as there are CPU cores. MaxScale versions older than 6 used one thread by default.

You can explicitly enable automatic configuration of this value by setting the value to auto. This way MariaDB MaxScale will detect the number of available processors and set the amount of threads to be equal to that number.

Note that if MaxScale is running in a container where the CPU resources have been limited, the use of auto may cause MaxScale to use more resources than what is available. In such a situation auto should not be used, but instead an explicit number that corresponds to the amount of CPU resources available in the container. As a rule of thumb, an appropriate value for threads is the vCPU of the container rounded up to the nearest integer. For instance, if the vCPU of the container is 0.5 then 1 is an appropriate value for threads, if the vCPU is 2.3 then 3 is.

The maximum value for threads is specified by threads_max.

# Valid options are:
#       threads=[<number of threads> | auto ]


From 23.02 onwards it is possible to change the number threads at runtime. Please see Threads for more details.

Additional threads will be created to execute other internal services within MariaDB MaxScale. This setting is used to configure the number of threads that will be used to manage the user connections.


  • Type: positive integer
  • Default: 256
  • Dynamic: No

This parameter specifies the hard limit for the number of worker threads, which is specified using threads.

At startup, if the value of threads is larger than that of threads_max, the value of threads will be reduced to that. At runtime, an attempt to increase the value of threads beyond that of threads_max is an error.


This duration parameter controls how often the load of the worker threads should be checked. The default value is 0, which means that no checks and no rebalancing will be performed.


Note that the value of rebalance_period should not be smaller than the value of rebalance_window whose default value is 10.

If the value of rebalance_period is significantly shorter than that of rebalance_window, it may lead to oscillation where work is constantly moved from one thread to another.


This integer parameter controls at which point MaxScale should start moving work from one worker thread to another.

If the difference in load between the thread with the maximum load and the thread with the minimum load is larger than the value of this parameter, then work will be moved from the former to the latter.

Although the load of a thread can vary between 0 and 100, the value of this parameter must be between 5 and 100. The default value is 20.


Note that rebalancing will not be performed unless rebalance_period has been specified.


This integer parameter controls how many seconds of load should be taken into account when deciding whether work should be moved from one thread to another.

The default value is 10, which means that the load during the last 10 seconds is considered when deciding whether work should be moved.

The minimum value is 1 and the maximum 60.


  • Type: boolean
  • Default: false
  • Dynamic: Yes

This parameter controls whether reverse domain name lookups are made to convert client IP addresses to hostnames. If enabled, client IP addresses will not be resolved to hostnames during authentication or for the REST API even if requested.

If you have database users that use a hostname in the host part of the user (i.e. 'user'@''), a reverse lookup on the client IP address is done to see if it matches the host. Reverse DNS lookups can be very slow which is why it is recommended that they are disabled and that users are defined using an IP address.


Duration, default 10s. This setting defines the connection timeout when attempting to fetch MariaDB/MySQL/Clustrix users from a backend server. The same value is also used for read and write timeouts. Increasing this value causes MaxScale to wait longer for a response from a server before user fetching fails. Other servers may then be attempted.


The value is given as a duration. If no explicit unit is provided, the value is interpreted as seconds. In subsequent versions a value without a unit may be rejected. Since the granularity of the timeout is seconds, a timeout specified in milliseconds will be rejected even if the given value is longer than a second.


Deprecated and ignored as of MaxScale 2.5.0. See auth_connect_timeout above.


Deprecated and ignored as of MaxScale 2.5.0. See auth_connect_timeout above.


The number of times an interrupted internal query will be retried. The default is to retry the query once. This feature was added in MaxScale 2.1.10 and was disabled by default until MaxScale 2.3.0.

An interrupted query is any query that is interrupted by a network error. Connection timeouts are included in network errors and thus is it advisable to make sure that the value of query_retry_timeout is set to an adequate value. Internal queries are only used to retrieve authentication data and monitor the servers.


The total timeout in seconds for any retried queries. The default value is 5 seconds.

An interrupted query is retried for either the configured amount of attempts or until the configured timeout is reached.

The value is specified as documented here. If no explicit unit is provided, the value is interpreted as seconds in MaxScale 2.4. In subsequent versions a value without a unit may be rejected. Note that since the granularity of the timeout is seconds, a timeout specified in milliseconds will be rejected, even if the duration is longer than a second.


  • Type: boolean
  • Default: false
  • Dynamic: Yes

Controls whether MaxScale is a passive node in a cluster of multiple MaxScale instances.

This parameter is intended to be used with multiple MaxScale instances that use failover functionality to manipulate the cluster in some form. Passive nodes only observe the clusters being monitored and take no direct actions.

The following functionality is disabled when passive mode is enabled:

  • Automatic failover in the mariadbmon module
  • Automatic rejoin in the mariadbmon module
  • Launching of monitor scripts

NOTE: Even if MaxScale is in passive mode, it will still accept clients and route any traffic sent to it. The only operations affected by the passive mode are the ones listed above.


  • Type: boolean
  • Default: false
  • Dynamic: Yes

Enable or disable the high precision timestamps in logfiles. Enabling this adds millisecond precision to all logfile timestamps.


  • Type: boolean
  • Default: false
  • Dynamic: Yes

Log messages to the system journal. This logs messages using the native SystemD journal interface. The logs can be viewed with journalctl.

MaxScale 22.08 changed the default value of syslog from true to false. This was done to remove the redundant logging that it caused as both syslog and maxlog were enabled by default. This caused each message to be logged twice: once into the system journal and once into MaxScale's own logfile.


  • Type: boolean
  • Default: true
  • Dynamic: Yes

Log messages to MariaDB MaxScale's log file. The name of the log file is maxscale.log and it is located in the directory pointed by logdir.


  • Type: boolean
  • Default: true
  • Dynamic: Yes

Log messages whose syslog priority is warning.

MaxScale logs warning level messages whenever a condition is encountered that the user should be notified of but does not require immediate action or it indicates a minor problem.


  • Type: boolean
  • Default: true
  • Dynamic: Yes

Log messages whose syslog priority is notice.

These messages contain information that is helpful for the user and they usually do not indicate a problem. These are logged whenever something worth nothing happens in either MaxScale or in the servers it monitors.


  • Type: boolean
  • Default: false
  • Dynamic: Yes

Log messages whose syslog priority is info.

These messages provide detailed information about the internal workings of MariaDB MaxScale. These messages should only be enabled when there is a need to inspect the internal logic of MaxScale. A common use-case is to see why a particular query was handled in a certain way. Almost all modules log some messages on the info level and this can be very helpful when trying to solve routing related problems.


  • Type: boolean
  • Default: false
  • Dynamic: Yes

Log messages whose syslog priority is debug.

These messages are intended for development purposes and are disabled by default. These are rarely useful outside of debugging core MaxScale issues.

Note: If MariaDB MaxScale has been built in release mode, then debug messages are excluded from the build and this setting will not have any effect. If an attempt to enable these is made, a warning is logged.


  • Type: boolean
  • Default: false
  • Dynamic: No

When enabled, a warning is logged whenever a client with SUPER-privilege successfully authenticates. This also applies to COM_CHANGE_USER-commands. The setting is intended for diagnosing situations where a client interferes with a primary server switchover. Super-users bypass the read_only-flag which switchover uses to block writes to the primary.


  • Type: integer
  • Default: 0
  • Dynamic: Yes

Enable or disable the augmentation of messages. If this is enabled, then each logged message is appended with the name of the function where the message was logged. This is primarily for development purposes and hence is disabled by default.

# Valid options are:
#       log_augmentation=<0|1>

To disable the augmentation use the value 0 and to enable it use the value 1.


It is possible that a particular error (or warning) is logged over and over again, if the cause for the error persistently remains. To prevent the log from flooding, it is possible to specify how many times a particular error may be logged within a time period, before the logging of that error is suppressed for a while.

# A valid value looks like
#       log_throttling = X, Y, Z
# where the first value X is a positive integer and means the number of times
# a specific error may be logged within a duration of Y, before the logging
# of that error is suppressed for a duration of Z.
log_throttling=8, 2s, 15000ms

In the example above, the logging of a particular error will be suppressed for 15 seconds if the error has been logged 8 times in 2 seconds.

The default is 10, 1000ms, 10000ms, which means that if the same error is logged 10 times in one second, the logging of that error is suppressed for the following 10 seconds.

Whenever an error message that is being throttled is logged within the triggering window (the second argument), the suppression window is extended. This continues until there is a pause in the messages that is longer than the triggering window.

For example, with the default configuration the messages must pause for at least one second in order for the throttling to eventually stop. This mechanism prevents long-lasting error conditions from slowly filling up the log with short bursts of messages.

To disable log throttling, add an entry with an empty value


or one where any of the integers is 0.

log_throttling=0, 0, 0

The durations can be specified as documented here. If no explicit unit is provided, the value is interpreted as milliseconds in MaxScale 2.4. In subsequent versions a value without a unit may be rejected.

Note that notice, info and debug messages are never throttled.


Set the directory where the logfiles are stored. The folder needs to be both readable and writable by the user running MariaDB MaxScale.

The default value is /var/log/maxscale/.



Set the directory where the data files used by MariaDB MaxScale are stored. Modules can write to this directory and for example the binlogrouter uses this folder as the default location for storing binary logs.

This is also the directory where the password encryption key is read from that is generated by maxkeys.

The default value is /var/lib/maxscale/.



  • Type: path
  • Mandatory: No
  • Dynamic: No
  • Default: ""

The location where the .secrets file is read from. If secretsdir is not defined, the file is read from datadir.

This parameter was added in MaxScale 6.4.16, 22.08.13, 23.02.10, 23.08.6 and 24.02.2.


Set the directory where MariaDB MaxScale looks for modules. The library directory is the only directory that MariaDB MaxScale uses when it searches for modules. If you have custom modules for MariaDB MaxScale, make sure you have them in this folder.

The default value depends on the operating system. For RHEL versions the value is /usr/lib64/maxscale/. For Debian and Ubuntu it is /usr/lib/x86_64-linux-gnu/maxscale/



Sets the directory where static data assets are loaded.

The MaxScale GUI static files are located in the gui/ subdirectory. If the GUI files have been manually moved somewhere else, this path must be configured to point to the parent directory of the gui/ subdirectory.

The MaxScale REST API only serves files for the GUI that are located in the gui/ subdirectory of the configured sharedir. Any files whose real path resolves to outside of this directory are not served by the MaxScale GUI: this is done to prevent other files from being accessible via the MaxScale REST API. This means that path to the GUI source directory can contain symbolic links but all parts after the /gui/ directory must reside inside it.

The default value is /usr/share/maxscale/.


Configure the directory MariaDB MaxScale uses to store cached data.

The default value is /var/cache/maxscale/.



Configure the directory for the PID file for MariaDB MaxScale. This file contains the Process ID for the running MariaDB MaxScale process.

The default value is /var/run/maxscale/.



Configure the directory where the executable files reside. All internal processes which are launched will use this directory to look for executable files.

The default value is /usr/bin/.



Location of the MariaDB Connector-C plugin directory. The MariaDB Connector-C used in MaxScale can use this directory to load authentication plugins. The versions of the plugins must be binary compatible with the connector version that MaxScale was built with.

Starting with version 6.2.0, the plugins are bundled with MaxScale and the default value now points to the bundled plugins. The location where the plugins are stored depends on the operating system. For RHEL versions the value is /usr/lib64/maxscale/plugin/. For Debian and Ubuntu it is /usr/lib/x86_64-linux-gnu/maxscale/plugin/.

Older versions of MaxScale used /usr/lib/mysql/plugin/ as the default value.



Configure the directory where persisted configurations are stored. When a new object is created via MaxCtrl, it will be stored in this directory. Do not use this directory for normal configuration files, use /etc/maxscale.cnf.d/ instead. The user MaxScale is running as must be able to write into this directory.

The default value is /var/lib/maxscale/maxscale.cnf.d/.



Configure the directory where module configurations are stored. Path arguments are resolved relative to this directory. This directory should be used to store module specific configurations.

Any configuration parameter that is not an absolute path will be interpreted as a relative path. The relative paths use the module configuration directory as the working directory.

For example, the configuration parameter file=my_file.txt would be interpreted as /etc/maxscale.modules.d/my_file.txt whereas file=/home/user/my_file.txt would be interpreted as /home/user/my_file.txt.

The default value is /etc/maxscale.modules.d/.



Set the folder where the errmsg.sys file is located in. MariaDB MaxScale will look for the errmsg.sys file installed with MariaDB MaxScale from this folder.

The default value is /var/lib/maxscale/.



Deprecated since MariaDB MaxScale 23.08.


Specifies the maximum size of the query classifier cache. The default limit is 15% of total system memory starting with MaxScale 2.3.7. In older versions the default limit was 40% of total system memory. This feature was added in MaxScale 2.3.0.

When the query classifier cache has been enabled, MaxScale will, after a statement has been parsed, store the classification result using the canonicalized version of the statement as the key.

If the classification result for a statement is needed, MaxScale will first canonicalize the statement and check whether the result can be found in the cache. If it can, the statement will not be parsed at all but the cached result is used.

The configuration parameter takes one integer that specifies the maximum size of the cache. The size of the cache can be specifed as explained here.

# 1MB query classifier cache

Note that MaxScale uses a separate cache for each worker thread. To obtain the amount of memory available for each thread, divide the cache size with the value of threads. If statements are evicted from the cache (visible in the diagnostic output), consider increasing the cache size.

Note also that limit is not a hard limit, but an approximate one. Namely, although the memory needed for storing the canonicalized statement and the classification result is correctly accounted for, there is additional overhead whose size is not exactly known and over which we do not have direct control.

Using maxctrl show threads it is possible to check what the actual size of the cache is and to see performance statistics.

Key Meaning
QC cache size The current size of the cache (bytes).
QC cache inserts How many entries have been inserted into the cache.
QC cache hits How many times the classification result has been found from the cache.
QC cache misses How many times the classification result has not been found from the cache, but the classification had to be performed.
QC cache evictions How many times a cache entry has had to be removed from the cache, in order to make place for another.


Deprecated since MariaDB MaxScale 23.08.


  • Type: boolean
  • Default: false
  • Dynamic: No

Enable or disable the substitution of environment variables in the MaxScale configuration file. If the substitution of variables is enabled and a configuration line like


is encountered, then $SOME_VALUE will be replaced with the actual value of the environment variable SOME_VALUE. Note: Variable substitution will be made only if '$' is the first character of the value. Everything following '$' is interpreted as the name of the environment variable. * Referring to a non-existing environment variable is a fatal error.


The setting of substitute_variables will have an effect on all parameters in the all other sections, irrespective of where the [maxscale] section is placed in the configuration file. However, in the [maxscale] section, to ensure that substitution will take place, place the substitute_variables=true line first.


Specifies whether the query classifier parser should initially expect MariaDB or PL/SQL kind of SQL.

The allowed values are: default: The parser expects regular MariaDB SQL. oracle : The parser expects PL/SQL.


The default value is default.

NOTE If sql_mode is set to oracle, then MaxScale will also assume that autocommit initially is off.

At runtime, MariaDB MaxScale will recognize statements like

set sql_mode=oracle;


set sql_mode=default;

and change mode accordingly.

NOTE If set sql_mode=oracle; is encountered, then MaxScale will also behave as if autocommit had been turned off and conversely, if set sql_mode=default; is encountered, then MaxScale will also behave as if autocommit had been turned on.

Note that MariaDB MaxScale is not explicitly aware of the sql mode of the server, so the value of sql_mode should reflect the sql mode used when the server is started.


What specific local address/interface to use when connecting to servers.

This can be used for ensuring that MaxScale uses a particular interface when connecting to servers, in case the computer MaxScale is running on has multiple interfaces.



How often, in seconds, MaxScale at most may refresh the users from the backend server.

MaxScale will at startup load the users from the backend server, but if the authentication of a user fails, MaxScale assumes it is because a new user has been created and will thus refresh the users. By default, MaxScale will do that at most once per 30 seconds and with this configuration option that can be changed. A value of 0 allows infinite refreshes and a negative value disables the refreshing entirely.


The value is specified as documented here. If no explicit unit is provided, the value is interpreted as seconds in MaxScale 2.4. In subsequent versions a value without a unit may be rejected. Note that since the granularity of the timeout is seconds, a timeout specified in milliseconds will be rejected, even if the duration is longer than a second.

In MaxScale 2.3.9 and older versions, the minimum allowed value was 10 seconds but, due to a bug, the default value was 0 which allowed infinite refreshes.


How often, in seconds, MaxScale will automatically refresh the users from the backend server.

This configuration is used to periodically refresh the backend users, making sure they are up to date. The default value for this setting is 0, meaning the users are not periodically refreshed. However, they can still be refreshed in case of failed authentication depending on users_refresh_time.


The value is specified as documented here. If no explicit unit is provided, the value is interpreted as seconds in MaxScale 2.4.


How many statements MaxScale should store for each session. This is for debugging purposes, as in case of problems it is often of value to be able to find out exactly what statements were sent before a particular problem turned up.

Note: See also dump_last_statements using which the actual dumping of the statements is enabled. Unless both of the parameters are defined, the statement dumping mechanism doesn't work.


Default is 0.


With this configuration item it is specified in what circumstances MaxScale should dump the last statements that a client sent. The allowed values are never, on_error and on_close. With never the statements are never logged, with on_error they are logged if the client closes the connection improperly, and with on_close they are always logged when a client session is closed.


Default is never.

Note that you need to specify with retain_last_statements how many statements MaxScale should retain for each session. Unless it has been set to another value than 0, this configuration setting will not have an effect.


How many log entries are stored in the session specific trace log. This log is written to disk when a session ends abnormally and can be used for debugging purposes. Currently the session trace log is written to the log in the following situations:

  • When MaxScale receives a fatal signal and is about to crash.
  • Whenever an unexpected response is read from a server
  • If the session is not closed gracefully (i.e. client doesn't send a COM_QUIT packet)
  • Whenever readwritesplit receives a responce that is was not expecting.

It would be good to enable this if a session is disconnected and the log is not detailed enough. In this case the info log might reveal the true cause of why the connection was closed.


Default is 0.

The session trace log is also exposed by REST API and is shown with maxctrl show sessions.

The order in which the session trace messages are logged into the log changed in MaxScale 6.4.9 (MXS-4716). Newer versions will log the messages in the "normal log order" of older events coming first and newer events appearing later in the file. Older versions of MaxScale logged the trace dump in the reverse order with the newest messages first and oldest ones last.


  • Type: regex
  • Default: none
  • Dynamic: Yes

If both session_trace and session_trace_match are defined, and a trace log entry of a session matches the regular expression, the trace log is written to disk. The check for the match is done when the session is stopping.

The most effective way to debug MaxScale related issues is to turn on log_info and observe the events written into the MaxScale log. The only problem with this approach is that it can cause a severe performance bottleneck and can easily fill up the disk as the amount of data written to it is significant. With session_trace and session_trace_match, the content that actually gets logged can be filtered to only what is needed.

For example, the following configuration would only log the trace log messages from sessions that execute SQL queries with syntax errors:

session_trace_match=/You have an error in your SQL syntax/

This could be used to easily identify which applications execute the queries without having to gather the info level log output from all the sessions that connect to MaxScale. For every session that ends up logging a syntax error message, the last 1000 lines of log output done by that session is written into the MaxScale log.


High water mark for network write buffer. When the size of the outbound network buffer in MaxScale for a single connection exceeds this value, network traffic throtting for that connection is started. The parameter accepts size type values. The default value is 65536 bytes (was 16777216 bytes before 22.08.4).

More specifically, if the client side write queue is above this value, it will block traffic coming from backend servers. If the backend side write queue is above this value, it will block traffic from client.

The buffer that this parameter controls is the buffer internal to MaxScale and is not the kernel TCP send buffer. This means that the total amount of buffered data is determined by both the kernel TCP buffers and the value of writeq_high_water.

Network throttling is only enabled when writeq_high_water is non-zero. In MaxScale 23.02 and earlier, also writeq_low_water had to be non-zero.


Low water mark for network write buffer. Once the traffic throttling is enabled, it will only be disabled when the network write buffer is below writeq_low_water bytes. The parameter accepts size type values. The default value is 1024 bytes (was 8192 bytes before 22.08.4).

The value of writeq_high_water must always be greater than the value of writeq_low_water.


  • Type: boolean
  • Default: true
  • Dynamic: No

Persist changes done at runtime. This parameter was added in MaxScale 22.08.0.

When persist_runtime_changes is enabled, runtime configuration changes done with the GUI, MaxCtrl or via the REST API cause a new configuration file to be saved in /var/lib/maxscale/maxscale.cnf.d/. If load_persisted_configs is enabled, these files will be applied on top of any existing values found in static configuration files whenever MaxScale is starting up.


  • Type: boolean
  • Default: true
  • Dynamic: No

Load persisted runtime changes on startup. This parameter was added in MaxScale 2.3.6.

All runtime configuration changes are persisted in generated configuration files located by default in /var/lib/maxscale/maxscale.cnf.d/ and are loaded on startup after main configuration files have been read. To make runtime configurations volatile (i.e. they are lost when maxscale is restarted), use load_persisted_configs=false. All changes are still persisted since it stores the current runtime state of MaxScale. This makes problem analysis easier if an unexpected outage happens.


The maximum number of authentication failures that are tolerated before a host is temporarily blocked. The default value is 10 failures. After a host is blocked, connections from it are rejected for 60 seconds. To disable this feature, set the value to 0.

Note that the configured value is not a hard limit. The number of tolerated failures is between max_auth_errors_until_block and threads * max_auth_errors_until_block where max_auth_errors_until_block is the configured value of this parameter and threads is the number of configured threads.


Define debug options from the --debug command line option. Either the command line option or the parameter should be used, not both. The debug options are only for testing purposes and are not to be used in production.

REST API Configuration

The MaxScale REST API is an HTTP interface that provides JSON format data intended to be consumed by monitoring appllications and visualization tools.

The following options must be defined under the [maxscale] section in the configuration file.


The network interface where the REST API listens on. The default value is the IPv4 address which only listens for local connections.


The port where the REST API listens on. The default value is port 8989.


  • Type: boolean
  • Default: true
  • Dynamic: No

Enable REST API authentication using HTTP Basic Access authentication. This is not a secure method of authentication without HTTPS but it does add a small layer of security.

For more information, read the REST API documentation.


The path to the TLS private key in PEM format for the admin interface.

If the admin_ssl_key and admin_ssl_cert options are all defined, the admin interface will use encrypted HTTPS instead of plain HTTP.


The path to the TLS public certificate in PEM format. See admin_ssl_key documentation for more details.


Deprecated since MariaDB MaxScale 22.08. See admin_ssl_ca.


The path to the TLS CA certificate in PEM format. If defined, the client certificate, if provided, will be validated against it. This parameter is optional starting with MaxScale 2.3.19.

NOTE Up until MariaDB MaxScale 6, the parameter was called admin_ssl_ca_cert, which is still accepted as an alias for admin_ssl_ca.


  • Type: enum_mask
  • Mandatory: No
  • Dynamic: No
  • Values: MAX, TLSv1.0, TLSv1.1, TLSv1.2, TLSv1.3, TLSv10, TLSv11, TLSv12, TLSv13
  • Default: MAX

This parameter controls the enabled TLS versions in the REST API. Accepted values are:

  • TLSv10
  • TLSv11
  • TLSv12
  • TLSv13 (not supported on OpenSSL 1.0)
  • MAX

MaxScale versions 6.4.16, 22.08.13, 23.02.10, 23.08.6, 24.02.2 and all newer releases accept also the following alias values:

  • TLSv1.0
  • TLSv1.1
  • TLSv1.2
  • TLSv1.3 (not supported on OpenSSL 1.0)

The default value is MAX which negotiates the highest level of encryption that both the client and server support. The list of supported TLS versions depends on the operating system and what TLS versions the GnuTLS library supports.

For example, to enable only TLSv1.1 and TLSv1.3, use admin_ssl_version=TLSv1.1,TLSv1.3.

This parameter was added in MaxScale 2.5.7.

Older versions of MaxScale interpreted admin_ssl_version as the minimum allowed TLS version. In those versions, admin_ssl_version=TLSv1.2 allowed both TLSv1.2 and TLSv1.3. In MaxScale 6.4.16, 22.08.13, 23.02.10, 23.08.6, 24.02.2 and all newer versions, the value is a enumeration of accepted TLS protocol versions. In these versions, admin_ssl_version=TLSv1.2 only allows TLSv1.2. To retain the old behavior, specify all the accepted values with admin_ssl_version=TLSv1.2,TLSv1.3


  • Type: boolean
  • Default: true
  • Dynamic: No

Enable or disable the admin interface. This allows the admin interface to be completely disabled to prevent access to it.


  • Type: boolean
  • Default: true
  • Dynamic: No

Enable or disable the admin graphical user interface.

MaxScale provides a GUI for administrative operations via the REST API. When the GUI is enabled, the root REST API resource (i.e. http://localhost:8989/) will serve the GUI. When disabled, the REST API will respond with a 200 OK to the request. By disabling the GUI, the root resource can be used as a low overhead health check.


  • Type: boolean
  • Default: true
  • Dynamic: No

Whether to serve the GUI only over secure HTTPS connections.

To be secure by default, the GUI is only served over HTTPS connections as it uses a token authentication scheme. This also controls whether the /auth endpoint requires an encrypted connection.

To allow use of the GUI without having to configure TLS certificates for the MaxScale REST API, set this parameter to false.


  • Type: boolean
  • Default: true
  • Dynamic: Yes

Log authentication failures for the admin interface.

admin_pam_readwrite_service and admin_pam_readonly_service

Use Pluggable Authentication Modules (PAM) for REST API authentication. The settings accept a PAM service name which is used during authentication if normal authentication fails. admin_pam_readwrite_service should accept users who can do any MaxCtrl/REST-API-operation. admin_pam_readonly_service should accept users who can only do read operations. Because REST-API does not support back and forth communication between the client and MaxScale, the PAM services must be simple. They should only ask for the password and nothing else.

If only admin_pam_readwrite_service is configured, both read and write operations can be authenticated by PAM. If only admin_pam_readonly_service is configured, only read operations can be authenticated by PAM. If both are set, the service used is determined by the requested operation. Leave or set both empty to disable PAM for REST-API.


  • Type: enum
  • Mandatory: No
  • Dynamic: No
  • Values: auto, HS256, HS384, HS512, RS256, RS384, RS512, PS256, PS384, PS512, ES256, ES384, ES512, ED25519, ED448
  • Default: auto

The signature algorithm used by the MaxScale REST API when generating JSON Web Tokens.

For more information about the tokens and how they work, refer to the REST API documentation.

If a symmetric algorithm is used (i.e. HS256, HS384 or HS512), MaxScale will generate a random encryption key on startup and use that to sign the messages. The symmetric key can also be retrieved from an Encryption Key Manager if the admin_jwt_key parameter is defined.

If an asymmetric algorithm (i.e. public key authentication) is used, both the admin_ssl_cert and admin_ssl_key parameters must be defined and they must contain a private key and a public certificate of the correct type. If the wrong key type, key length or elliptic curve is used, MaxScale will refuse to start.

Asymmetric key algorithms make it possible for the clients of the REST API to validate that the token was indeed generated by the correct entity.

Symmetric algorithms make it easy to share the same tokens between multiple MaxScale instaces as the shared secret can be stored in a key management system.

The possible values for this parameter are:

  • auto

  • MaxScale will attempt to detect the best algorithm to use for signatures. The algorithm used depends on the private key type: RSA keys use PS256, EC keys use the ES256, ES384 or ES512 depending on the curve, Ed25519 keys use ED25519 and Ed448 keys uses ED448. If MaxScale cannot auto-detect the key type, it falls back to HS256 as the default algorithm.

  • HS256, HS384 or HS512

  • HMAC with SHA-2 Functions. If admin_jwt_key is not defined, uses a random encryption key of the correct size.

  • RS256, RS384 or RS512

  • Digital Signature with RSASSA-PKCS1-v1_5. Requires at least a 2048-bit RSA key.

  • PS256, PS384 or PS512

  • Digital Signature with RSASSA-PSS. Requires at least a 2048-bit RSA key.

  • ES256, ES384 or ES512

  • Digital Signature with ECDSA. Requires an EC key with the correct curve: P-256 for ES256, P-384 for ES384 and P-512 for ES512.

  • ED25519 or ED448

  • Edwards-curve Digital Signature Algorithm (EdDSA). Requires a Ed25519 key for ED25519 or a Ed448 key for ED448.


  • Type: string
  • Mandatory: No
  • Dynamic: No
  • Default: ""

The ID for the encryption key used to sign the JSON Web Tokens. If configured, an Encryption Key Manager must also be configured and it must contain the key with the given ID. If no key is defined, MaxScale will use a random encryption key whenever a symmetric signature algorithm is used.

Currently, the encryption key is only read on startup. This means that the tokens will be signed by the latest key version that is available on startup: rotating the encryption key in the key management system will not cause the JWTs to be signed with newer versions of the key.


  • Type: duration
  • Mandatory: No
  • Dynamic: No
  • Default: 24h

The maximum lifetime of a token generated by the /auth endpoint.

If a client requests for a token with a lifetime that exceeds the configured value, the token lifetime is silently truncated to this value. This can be used to control the maximum length of a MaxGUI session.

This also acts as the effective maximum age of any database connection created from the /sql endpoint.


  • Type: string
  • Mandatory: No
  • Dynamic: No
  • Default: ""

The URL to a OpenID Connect server that is used for JWT validation.

If defined, any tokens signed by this server are accepted as valid bearer tokens for the MaxScale REST API. The "sub" field of the token is assumed to be the username of an administrative user in MaxScale and the "account" claim is assumed to be the type of the user: "admin" for administrative users with full access to the REST-API and "basic" for users with read-only access to the REST-API. This means that all users must be first created with maxctrl create user before the tokens are accepted if the OIDC provider is not able to add the "account" claim.

If this URL is changed at runtime, the new certificates will not be fetched until a maxctrl reload tls command is executed.


  • Type: string
  • Mandatory: No
  • Dynamic: No
  • Default: ""

URL to a server to which the REST API token verification is delegated.

If the URL is defined, any tokens passed to the REST API will be validated by doing a GET request to the URL with the client's token as a bearer token. The Referer header of the request is set to the URL being requested by the client and the custom X-Referrer-Method header is set to the HTTP method being used (PUT, GET etc.).

Note: When admin_verify_url is used and the remote server cannot be accessed, all REST API access that uses tokens will be disabled. The only way to use the REST API with tokens is to remove admin_verify_url from the configuration which requires restarting MaxScale. The REST API still accepts HTTP Basic Access authentication even if the remote server cannot be reached.

By delegating the authentication and authorization of the REST API to an external server, users can implement custom access control systems for the MaxScale REST API.


  • Type: string
  • Mandatory: No
  • Dynamic: No
  • Default: maxscale

The issuer ("iss") claim of all JWTs generated by MaxScale. This can be set to a custom value to uniquely identify which MaxScale issued a JWT. This is especially useful for cases where the MaxScale GUI is used from behind a reverse proxy.


  • Type: boolean
  • Mandatory: No
  • Dynamic: Yes
  • Default: false

Enable logging of incoming REST API calls.


  • Type: string
  • Mandatory: No
  • Dynamic: Yes
  • Default: /var/log/maxscale/admin_audit.csv

The file where the REST API auditing information is logged.

If a non-default value is used, the directory where the file resides must exist. For example, with /var/log/maxscale/audit_files/audit.csv, the directory /var/log/maxscale/audit_files must exist.


  • Type: enum
  • Mandatory: No
  • Dynamic: Yes
  • Default: No exclusions

List of comma separated HTTP methods to exclude from logging Currently MaxScale does not use CONNECT or TRACE.

Resetting to log all methods can be done in the configuration file by writing admin_audit_exclude_methods= or at runtime with maxctrl alter maxscale admin_audit_exclude_methods=. Remember that once a runtime change has been made, the entry for that setting is ignored in the main configuration file (usually maxscale.cnf).


  • Type: monitor
  • Default: No default value
  • Dynamic: Yes

This parameter controls which cluster (i.e. monitor) is used to synchronize configuration changes between MaxScale instances. The first server labeled Master will be used for the synchronization.

By default configuration synchronization is not enabled and it must be explicitly enabled by defining a monitor name for config_sync_cluster.

When config_sync_cluster is defined, config_sync_user and config_sync_password must also be defined.

For a detailed description of this feature, refer to the Configuration Synchronization section.


  • Type: string
  • Default: No default value
  • Dynamic: Yes

The username for the account that is used to synchronize configuration changes across MaxScale instances. Both this parameter and config_sync_password are required if config_sync_cluster is configured.

This account must have the following grants:

GRANT SELECT, INSERT, UPDATE, CREATE ON `mysql`.`maxscale_config`

The mysql.maxscale_config table can be pre-created in which case the CREATE grant is not needed by the user configured in config_sync_user. The following SQL is used to create the table.

CREATE TABLE IF NOT EXISTS mysql.maxscale_config(
  cluster VARCHAR(256) PRIMARY KEY,
  version BIGINT NOT NULL,
  config JSON NOT NULL,
  origin VARCHAR(254) NOT NULL,

If the database where the table is created is changed with config_sync_db, the grants must be adjusted to target that database instead.


  • Type: password
  • Default: No default value
  • Dynamic: Yes

The password for config_sync_user. Both this parameter and config_sync_user are required if config_sync_cluster is configured. This password can optionally be encrypted using maxpasswd.


  • Type: string
  • Default: mysql
  • Dynamic: No

The database where the maxscale_config table is created. By default the table is created in the mysql database. This parameter was added in MaxScale versions 6.4.6 and 22.08.5.

As tables in the mysql database cannot have triggers on them, the database must be changed to a user-created one in order to create triggers on the table. An example use-case for triggers on this table is to track all configuration changes done to MaxScale by inserting them into a separate table.


  • Type: duration
  • Default: 5s
  • Dynamic: Yes

How often to synchronize the configuration with the cluster.

As the synchronization involves selecting the configuration version from the database, this value should not be set to an unreasonably low value. The default value of 5 second should provide a good compromise between responsiveness and how much load it places on the database.


  • Type: duration
  • Default: 10s
  • Dynamic: Yes

Timeout for all SQL operations done during the configuration synchronization. If an operation exceeds this timeout, the configuration change is treated as failed and an error is reported to the client that did the change.


  • Type: enum
  • Dynamic: Yes
  • Values: none, file, kmip, vault
  • Default: none

The encryption key manager to use. The available encryption key managers are:

Refer to the Encryption Key Managers section for more information on how to configure the key managers. The key managers each have their configuration in their own namespace and must have their name as a prefix.

For example to configure the file key manager, the following must be used:



MaxScale logs warnings and errors for various reasons and often it is self- evident and generally applicable whether some occurence should warrant a warning or an error, or perhaps just an info-level message.

However, there are events whose seriousness is not self-evident. For instance, in some environments an authentication failure may simply indicate that someone has made a typo, while in some other environment that can only happen in case there has been a security breech.

To handle events like these, MaxScale defines events whose logging facility and level can be controlled by the administrator. Given an event X, its facility and level are controlled in the following manner:


The above means that if event X occurs, then that is logged using the facility LOG_LOCAL0 and the level LOG_ERR.

The valid values of facilityare the facility values reported byman syslog, e.g.LOG_AUTH,LOG_LOCAL0andLOG_USER. Likewise, the valid values forlevelare the ones also reported byman syslog, e.g.LOG_WARNING,LOG_ERRandLOG_CRIT`.

Note that MaxScale does not act upon the level, that is, even if the level of a particular event is defined to be LOG_EMERG, MaxScale will not shut down if that event occurs.

The default facility is LOG_USER and the default level is LOG_WARNING.

Note that you may also have to configure rsyslog to ensure that the event can be logged to the intended log file. For instance, if the facility is chosen to be LOG_AUTH, then /etc/rsyslog.conf should contain a line like

auth,authpriv.*                 /var/log/auth.log

for the logged events to end up in /var/log/auth.log, where the initial auth is the relevant entry.

The available events are:


This event occurs when there is an authentication failure.



A service represents the database service that MariaDB MaxScale offers to the clients. In general a service consists of a set of backend database servers and a routing algorithm that determines how MariaDB MaxScale decides to send statements or route connections to those backend servers.

A service may be considered as a virtual database server that MariaDB MaxScale makes available to its clients.

Several different services may be defined using the same set of backend servers. For example a connection based routing service might be used by clients that already performed internal read/write splitting, whilst a different statement based router may be used by clients that are not written with this functionality in place. Both sets of applications could access the same data in the same databases.

A service is identified by a service name, which is the name of the configuration file section and a type parameter of service.


In order for MariaDB MaxScale to forward any requests it must have at least one service defined within the configuration file. The definition of a service alone is not enough to allow MariaDB MaxScale to forward requests however, the service is merely present to link together the other configuration elements.


The router parameter of a service defines the name of the router module that will be used to implement the routing algorithm between the client of MariaDB MaxScale and the backend databases. Additionally routers may also be passed a comma separated list of options that are used to control the behavior of the routing algorithm. The two parameters that control the routing choice are router and router_options. The router options are specific to a particular router and are used to modify the behavior of the router. The read connection router can be passed options of master, slave or synced, an example of configuring a service to use this router and limiting the choice of servers to those in slave state would be as follows.


To change the router to connect on to servers in the master state as well as slave servers, the router options can be modified to include the master state.


A more complete description of router options and what is available for a given router is included with the documentation of the router itself.


Option string given to the router module. The value of this parameter should be a comma-separated list of key-value pairs. See router specific documentation for more details.


The filters option allow a set of filters to be defined for a service; requests from the client are passed through these filters before being sent to the router for dispatch to the backend server. The filters parameter takes one or more filter names, as defined within the filter definition section of the configuration file. Multiple filters are separated using the | character.

filters=counter | QLA

The requests pass through the filters from left to right in the order defined in the configuration parameter.


The targets parameter is a comma separated list of server and/or service names that comprise the routing targets of the service. This parameter was added in MaxScale 2.5.0.


This parameter allows nested service configurations to be defined without having to configure listeners for all services. For example, one use-case is to use multiple readwritesplit services behind a schemarouter service to have both the sharding of schemarouter with the high-availability of readwritesplit.

NOTE: The targets parameter is mutually exclusive with the cluster and servers parameters.


The servers parameter in a service definition provides a comma separated list of the backend servers that comprise the service. The server names are those used in the name section of a block with a type parameter of server (see below).


NOTE: The servers parameter is mutually exclusive with the cluster and targets parameters.


The servers the service uses are defined by the monitor specified as value of this configuration parameter.


NOTE: The cluster parameter is mutually exclusive with the servers and targets parameters.

user and password

These settings define the credentials the service uses to fetch user account information from backends. The password may be either a plain text password or an encrypted password.


See MySQL protocol authentication documentation for more information (such as required grants) and troubleshooting tips regarding user account management and client authentication.

From 23.08.0 onwards, MaxScale will remember the previous password when the password is changed. If the fetching of the user account information fails using the new password, it will be attempted using the previous one. The purpose of this change is to make it a smoother operation to change the password of the service user. The steps are as follows:

  1. $ maxctrl alter service MyService password=TheNewPassword
  2. MariaDB [(none)]> set password for TheServiceUser = password('TheNewPassword');

Since the old password is remembered and used if the new password does not work, it is no longer necessary to perform those steps simultaneously.


  • Type: boolean
  • Default: false
  • Dynamic: Yes

This parameter controls the ability of the root user to connect to MariaDB MaxScale and hence onwards to the backend servers via MariaDB MaxScale.


Deprecated and ignored.


This parameter sets a custom version string that is sent in the MySQL Handshake from MariaDB MaxScale to clients.



If not set, MaxScale will attempt to use a version string from the backend databases by selecting the version string of the database with the lowest version number. If the selected version is from the MariaDB 10 series, a 5.5.5- prefix will be added to it similarly to how the MariaDB 10 series versions added it.

If MaxScale has not been able to connect to a single database and the versions are unknown, the default value of 5.5.5-10.4.32 <MaxScale version>-maxscale is used where <MaxScale version> is the version of MaxScale.


  • Type: boolean
  • Default: false
  • Dynamic: Yes

This parameter controls whether only a single server or all of the servers are used when loading the users from the backend servers.

By default MaxScale uses the first server labeled as Master as the source of the authentication data. When this option is enabled, the authentication data is loaded from all the servers and combined into one big data set.


  • Type: boolean
  • Default: true
  • Dynamic: Yes

Note: This parameter has been deprecated in MaxScale 23.08. The stripping of escape characters is in all known cases the correct thing to do.

This setting controls whether escape characters (\) are removed from database names when loading user grants from a backend server. When enabled, a grant such as grant select on `test\_`.* to 'user'@'%'; is read as grant select on `test_`.* to 'user'@'%';

This setting has no effect on database-level grants fetched from a MariaDB Server. The database names of a MariaDB Server are compared using the LIKE operator to properly handle wildcards and escaped wildcards. This setting may affect database names in table and column level grants, although these typically do not contain backlashes.

Some visual database management tools automatically escape some characters and this might cause conflicts when MaxScale tries to authenticate users.


  • Type: boolean
  • Default: true
  • Dynamic: Yes

Enable or disable the logging of authentication failures and warnings. If enabled, messages about failed authentication attempts will be logged with details about who tried to connect to MariaDB MaxScale and from where.


  • Type: boolean
  • Default: false
  • Dynamic: Yes

When enabled, this allows a service to log warning messages even if the global log level configuration disables them.

Note that disabling the service level logging does not override the global logging configuration: with log_warning=false in the service and log_warning=true globally, warnings will still be logged for all services.


  • Type: boolean
  • Default: false
  • Dynamic: Yes

When enabled, this allows a service to log notice messages even if the global log level configuration disables them.


  • Type: boolean
  • Default: false
  • Dynamic: Yes

When enabled, this allows a service to log info messages even if the global log level configuration disables them.


  • Type: boolean
  • Default: false
  • Dynamic: Yes

When enabled, this allows a service to log debug messages even if the global log level configuration disables them.

Debug messages are only enabled for debug builds. Enabling log_debug in a release build does nothing.


  • Type: duration
  • Default: 0s
  • Mandatory: No
  • Dynamic: Yes
  • Auto tune: Yes

The wait_timeout parameter is used to disconnect sessions to MariaDB MaxScale that have been idle for too long. The session timeouts are disabled by default. To enable them, define the timeout in seconds in the service's configuration section. A value of zero is interpreted as no timeout, the same as if the parameter is not defined.

This parameter used to be called connection_timeout and this name is still accepted as an alias for wait_timeout. The old name has been deprecated in MaxScale 23.08.

Note that since the granularity of the timeout is seconds, a timeout specified in milliseconds will be rejected, even if the duration is longer than a second.

This parameter only takes effect in top-level services. A top-level service is the service where the listener that the client connected to points (i.e. the value of service in the listener). If a service defines other services in its targets parameter, the wait_timeout for those is not used.

The value of wait_timeout in MaxScale should be lower than the lowest wait_timeout value on the backend servers. This way idle clients are disconnected by MaxScale before the backend servers have to close them. Any client-side idle timeouts (e.g. maximum lifetime for connection pools) should be lower than wait_timeout in both MaxScale and MariaDB. This way the client application will end up closing the connection itself which most of the time results in better and more helpful error messages.

Warning: If a connection is idle for longer than the configured connection timeout, it will be forcefully disconnected and a warning will be logged in the MaxScale log file.




The maximum number of simultaneous connections MaxScale should permit to this service. If the parameter is zero or is omitted, there is no limit. Any attempt to make more connections after the limit is reached will result in a "Too many connections" error being returned.

Warning: In MaxScale 2.5, it is possible that the number of concurrent connections temporarily exceeds the value of max_connections. This has been fixed in MaxScale 6.




  • Type: boolean
  • Default: false
  • Dynamic: Yes

*Note: This parameter has been deprecated in MaxScale 23.08 as the feature is now used automatically if needed. In addition, the session tracking no longer needs to be enabled in MariaDB for the transaction state tracking to work correctly.

Enable transaction state tracking by offloading it to the backend servers. Getting the transaction state from the server will be more accurate for stored procedures or multi-statement SQL that modifies the transaction state non-atomically.

In general, it is better to avoid using this type of SQL as tracking the transaction state via the server responses is not compatible with features such as transaction_replay in readwritesplit. session_track_trx_state should only be enabled if the default transaction tracking done by MaxScale does not produce the desired outcome.

This is only supported by MariaDB versions 10.3 or newer. The following must be configured in the MariaDB server in order for this feature to work. Not configuring the MariaDB server with it can result in the transaction state being wrong in MaxScale which can result in data inconsistency.

session_track_state_change = ON
session_track_transaction_info = CHARACTERISTICS


How many statements MaxScale should store for each session of this service. This overrides the value of the global setting with the same name. If retain_last_statements has been specified in the global section of the MaxScale configuration file, then if it has not been explicitly specified for the service, the global value holds, otherwise the service specific value rules. That is, it is possible to enable the setting globally and turn it off for a specific service, or just enable it for specific services.

The value of this parameter can be changed at runtime using maxctrl and the new value will take effect for sessions created thereafter.

maxctrl alter service MyService retain_last_statements 5


  • Type: duration
  • Default: 300s
  • Mandatory: No
  • Dynamic: Yes
  • Auto tune: Yes

Keep idle connections alive by sending pings to backend servers. This feature was introduced in MaxScale 2.5.0 where it was changed from a readwritesplit-specific feature to a generic service feature. The default value for this parameter is 300 seconds. To disable this feature, set the value to 0.

The keepalive interval is specified as documented here. If no explicit unit is provided, the value is interpreted as seconds in MaxScale 2.5. In subsequent versions a value without a unit may be rejected. Note that since the granularity of the keepalive is seconds, a keepalive specified in milliseconds will be rejected, even if the duration is longer than a second.

The parameter value is the interval in seconds between each keepalive ping. A keepalive ping will be sent to a backend server if the connection has been idle for longer than the configured keepalive interval.

Starting with MaxScale 2.5.21 and 6.4.0, the keepalive pings are not sent if the client has been idle for longer than the configured value of connection_keepalive. Older versions of MaxScale sent the keepalive pings regardless of the client state.

This parameter only takes effect in top-level services. A top-level service is the service where the listener that the client connected to points (i.e. the value of service in the listener). If a service defines other services in its targets parameter, the connection_keepalive for those is not used.

If the value of connection_keepalive is changed at runtime, the change in the value takes effect immediately.

As the connection keepalive pings must be done only when there's no ongoing query, all requests and responses must be tracked by MaxScale. In the case of readconnroute, this will incur a small drop in performance. For routers that rely on result tracking (e.g. readwritesplit and schemarouter), the performance will be the same with or without connection_keepalive.

If you want to avoid the performance cost and you don't need the connection keepalive feature, you can disable it with connection_keepalive=0s.


  • Type: boolean
  • Default: false
  • Dynamic: Yes

By default, connection keepalive pings are only sent if the client is either executing a query or has been idle for less than the duration configured in connection_keepalive. When this parameter is enabled, keepalive pings are unconditionally sent to any backends that have been idle for longer than connection_keepalive seconds. This option was added in MaxScale 6.4.9 and can be used to emulate the pre-2.5.21 behavior if long-lived application connections rely on the old unconditional keepalive pings.

Note: if force_connection_keepalive is enabled and connection_keepalive in MaxScale is set to a lower value than the wait_timeout on the database, the client idle timeouts that wait_timeout control are no longer effective. This happens because MaxScale unconditionally sends the pings which make the client behave like it is not idle and thus the connections will never be killed due to wait_timeout.


This parameter controls how long a network write to the client can stay buffered. This feature is disabled by default.

When net_write_timeout is configured and data is buffered on the client network connection, if the time since the last successful network write exceeds the configured limit, the client connection will be disconnected.

The value is specified as documented here. If no explicit unit is provided, the value is interpreted as seconds in MaxScale 2.4. In subsequent versions a value without a unit may be rejected. Note that since the granularity of the timeout is seconds, a timeout specified in milliseconds will be rejected, even if the duration is longer than a second.


  • Type: integer
  • Default: 50
  • Dynamic: Yes

max_sescmd_history sets a limit on how many distinct session commands are stored in the session command history. When the history limit is exceeded, the history is either pruned to the last max_sescmd_history command (when prune_sescmd_history is enabled) or the history is disabled and server reconnections are no longer possible.

The required history size can be estimated by counting the total number of prepared statements and session state modifying commands (e.g SET NAMES) that are used by a client. Note that connectors usually add some commands that aren't visible to the application developer which means a safety margin should be added. A good rule of thumb is to count the expected number of statements and double that number.

This parameter was moved into the MaxScale core in MaxScale 6.0. The parameter can be configured for all routers that support the session command history. Currently only readwritesplit and schemarouter support it.


  • Type: boolean
  • Default: true
  • Dynamic: Yes

This option enables pruning of the session command history when it exceeds the value configured in max_sescmd_history. When this option is enabled, only a set number of statements are stored in the history. This limits the per-session memory use while still allowing safe reconnections.

This parameter is intended to be used with pooled connections that remain in use for a very long time. Most connection pool implementations do not reset the session state and instead re-initialize it with new values. This causes the session command history to grow at roughly a constant rate for the lifetime of the pooled connection.

Starting with MaxScale 23.08, the session command history is also simplified before being stored. The simplification is done by removing repeated occurrences of the same command and only executing the latest one of them. The order in which the commands are executed still remains the same but inter-dependencies between commands are not preserved.

For example, the following set of commands demonstrates how the history simplification works and how inter-dependencies can be lost.

SET @my_planet='Earth';                            -- This command will be removed by history simplification
SET @my_home='My home is: ' || @my_planet;         -- Command #1 in the history
SET @my_planet='Earth';                            -- Command #2 in the history

In the example, the value of @my_home has a dependency on the value of @my_planet which is lost when the same statement is executed again and the history simplification removes the earlier one.

This same problem can occur even in older versions of MaxScale that used a sliding window of the history when the window moves past the statement that later statement dependend on. If inter-dependent session commands are being used, the history pruning should be disabled.

Each client-side session that uses a pooled connection only executes a finite amount of session commands. By retaining a shorter history that encompasses all session commands the individual clients execute, the session state of a pooled connection can be accurately recreated on another server.

When the session command history pruning is enabled, there is a theoretical possibility that upon server reconnection the session states of the connections are inconsistent. This can only happen if the length of the stored history is shorter than the list of relevant statements that affect the session state. In practice the default value of 50 session commands is a fairly reasonable value and the risk of inconsistent session state is relatively low.

In case the default history length is too short for safe pruning, set the value of max_sescmd_history to the total number of commands that affect the session state plus a safety margin of 10. The safety margin reserves some extra space for new commands that might be executed due to changes in the client side application.

This parameter was moved into the MaxScale core in MaxScale 6.0. The parameter can be configured for all routers that support the session command history. Currently only readwritesplit and schemarouter support it.


  • Type: boolean
  • Default: false
  • Dynamic: Yes

This option disables the session command history. This way no history is stored and if a replica server fails, the router will not try to replace the failed replica. Disabling session command history will allow long-lived connections without causing a constant growth in the memory consumption.

This parameter should only be used when either the memory footprint must be as small as possible or when the pruning of the session command history is not acceptable.

This parameter was moved into the MaxScale core in MaxScale 6.0. The parameter can be configured for all routers that support the session command history. Currently only readwritesplit and schemarouter support it.


Defines path to a file with additional user accounts for incoming clients. Default value is empty, which disables the feature.


In addition to querying the backends, MaxScale can read users from a file. This feature is useful when backends have limitations on the type of users that can be created, or if MaxScale needs to allow users to log in even when backends are down (e.g. binlog router). The users read from the file are only present on MaxScale, so logging into backends can still fail. The format of the file is protocol-specific. The following only applies to MariaDB-protocol, which is also the only protocol supporting this feature.

The file contains json text. Three objects are read from it: user, db and roles_mapping, none of which are mandatory. These objects must be arrays which contain user information similar to the mysql.user, mysql.db and mysql.roles_mapping tables on the server. Each array element must define at least the string fields user and host, which define the user account to add or modify.

The elements in the user-array may contain the following additional fields. If a field is not defined, it is assumed either empty (string) or false (boolean).

  • password: String. Password hash, similar to the equivalent column on server.
  • plugin: String. Authentication plugin used by client, similar to server.
  • authentication_string: String. Additional authentication info, similar to server.
  • default_role: String. Default role of user, similar to server.
  • super_priv: Boolean. True if user has SUPER grant.
  • global_db_priv: Boolean. True if user can access any database on login.
  • proxy_priv: Boolean. True if user has a PROXY grant.
  • is_role: Boolean. True if user is a role.

The elements in the db-array must contain the following additional field:

  • db: String. Database which the user can access. Can contain % and _ wildcards.

The elements in the roles_mapping-array must contain the following additional field:

  • role: String. Role the user can access.

When users are read from both servers and the file, the server takes priority. That is, if user 'joe'@'%' is defined on both, the file-version is discarded. The file can still affect the database grants and roles of 'joe'@'%', as the db and roles_mapping-arrays are read separately and added to existing grant and role lists.

An example users file is below.

    "user": [
            "user": "test1",
            "host": "%",
            "global_db_priv": true
            "user": "test2",
            "host": "",
            "password": "*032169CDF0B90AF8C00992D43D354E29A2EACB42",
            "plugin": "mysql_native_password",
            "default_role": "role2"
            "user": "",
            "host": "%",
            "plugin": "pam",
            "proxy_priv": true
    "db": [
            "user": "test2",
            "host": "",
            "db": "test"
    "roles_mapping": [
            "user": "test2",
            "host": "",
            "role": "role2"


Defines when user_accounts_file is read. The value is an enum, either "add_when_load_ok" (default) or "file_only_always".

"add_when_load_ok" means that the file is only read when users are successfully read from a server. The file contents are then added to the server-based data. If reading from server fails (e.g. servers are down), the file is ignored.

"file_only_always" means that users are not read from the servers at all and the file contents is all that matters. The state of the servers is ignored. This mode can be useful with the binlog router, as it allows clients to log in and fetch binary logs from MaxScale even when backend servers are down.



Time, default: -1s. Normally, MaxScale only pools backend connections when a session is closed (controlled by server settings persistpoolmax and persistmaxtime). Other sessions can use the pooled connections instead of creating new connections to backends. If connection sharing is enabled, MaxScale can pool backend connections also from running sessions, and re-attach a pooled connection when a session is doing a query. This effectively allows multiple sessions to share backend connections.

idle_session_pool_time defines the amount of time a session must be idle before its backend connections may be pooled. To enable connection sharing, set idle_session_pool_time to zero or greater. The value can be given in seconds or milliseconds.

This feature has a significant drawback: when a backend connection is reused, it needs to be restored to the correct state. This means reauthenticating and replaying session commands. This can add a significant delay before the connection is actually ready for a query. If the session command history size exceeds the value of max_sescmd_history, connection sharing is disabled for the session.

This feature should only be used when limiting the backend connection count is a priority, even at the cost of query delay and throughput. This feature only works when the following server settings are also set in MaxScale configuration:

  1. max_routing_connections
  2. persistpoolmax
  3. persistmaxtime

Since reusing a backend connection is an expensive operation, MaxScale only pools connections when another session requires them. idle_session_pool_time thus effectively limits the frequency at which a connection can be moved from one session to another. Setting idle_session_pool_time=0ms causes MaxScale to move connections as soon as possible.


See below for more information on configuring connection sharing.

Details, limitations and suggestions for connection sharing

As noted above, when a connection is pooled and reused its state is lost. Although session variables and prepared statements are restored by replaying session commands, some state information cannot be transferred.

The most common such state is a transaction. When a transaction is on, connection sharing is disabled for that session until the transaction completes. Other similar situations may not be properly detected, and it's the responsibility of the user to avoid introducing such state to the session when using connection sharing. This means that the following should not be used:

  • Statements such as LOCK TABLES and GET LOCK or any other statement that introduces state into the connection.

  • Temporary tables and some problematic user or session variables such as LAST_INSERT_ID(). For LAST_INSERT_ID(), the value returned by the connector must be used instead of the variable.

  • Stored procedures that cause session level side-effects.

Several settings affect connection sharing and its effectiveness. Reusing a connection is an expensive operation so its frequency should be minimized. The important configuration settings in addition to idle_session_pool_time are MaxScale server settings persistpoolmax, persistmaxtime and max_routing_connections. The service settings max_sescmd_history, prune_sescmd_history and multiplex_timeout also have an effect. These settings should be tuned according to the use case.

persistpoolmax limits how many connections can be kept in a pool for a given server. If the pool is full, no more connections are detached from sessions even if they are idle and required. The pool size should be large enough to contain any connections being transferred between sessions, but not be greater than max_routing_connections. Using the value of max_routing_connections is a reasonable starting point.

persistmaxtime limits the time a connection may stay in the pool. This should be high enough so that pooled connections are not unnecessarily closed. Cleaning up clearly unneeded connections from the pool may be useful when max_routing_connections is restrictively tuned. Because each MaxScale routing thread has its own connection pool, one thread can monopolize access to a server. For example, if the pool of thread 1 has 100 connections to ServerA with max_routing_connections=100, other threads can no longer connect to the server. In such a situation, reducing persistmaxtime of ServerA may help as it would cause unneeded connections in the pool to be closed faster. Such connection slots then become available to other routing threads. Reducing the number of routing threads may also help, as it reduces pool fragmentation. This may reduce overall throughput, though. When using connection sharing, backend connections are only in the pool momentarily. Consequently, persistmaxtime can be set quite low, e.g. 10s.

If a client session exceeds max_sescmd_history (default 50), pooling is disabled for that session. If many sessions do this and max_routing_connections is set, other sessions will stall as they cannot find a backend connection. This can be avoided with prune_sescmd_history. However, pruning means that old session commands will not be replayed when a pooled connection is reused. If the pruned commands are important (e.g. statement preparations), the session may fail later on.

If the number of clients actively running queries is greater than max_routing_connections, query throughput will suffer as clients will need to take turns. In this situation, it's imperative to minimize the number of backend connections a single session uses. The settings to achieve this depend on the router. For ReadWriteSplit the following should be used:


The above settings mean that MaxScale can process roughly (number of replica servers X max_routing_connections) read queries simultaneously. Write queries will still need to take turns as there is only one primary server.

The following configuration snippet shows example server and service configurations for connection sharing with ReadWriteSplit.

max_routing_connections=1000 #this should be based on MariaDB Server capacity
persistpoolmax=1000 #same as above
#other server settings...

#other service settings...


Time, default: 60s. When connection sharing (as described above) is on, clients may have to wait for their turn to use a backend connection. If too much time passes without a connection becoming available, MaxScale returns an error to the client, usually also ending the session. multiplex_timeout sets this timeout. Increase it if queries are failing with "Timed out when waiting for a connection". Decrease it if failing early is preferable to stalling.



Server sections define the backend database servers MaxScale uses. A server is identified by its section name in the configuration file. The only mandatory parameter of a server is type, but address and port are also usually defined. A server may be a member of one or more services. A server may only be monitored by at most one monitor.



The IP-address or hostname of the machine running the database server. MaxScale uses this address to connect to the server. This parameter is mandatory unless socket is defined.


The port the backend server listens on for incoming connections. MaxScale uses this port to connect to the server. The default value is 3306.


The absolute path to a UNIX domain socket the MariaDB server is listening on. Either address or socket must be defined and defining them both is an error.

monitoruser and monitorpw

These settings define a server-specific username and password for monitoring the server. Monitors typically use the credentials in their own configuration sections to connect to all servers. If server-specific settings are given, the monitor uses those instead.


monitorpw may be either a plain text password or an encrypted password. See the section encrypting passwords for more information.


An alternative port used for administrative connections to the server. If this setting is defined, MaxScale uses it for monitoring the server and to fetch user accounts. Client sessions will still use the normal port.

Defining extra_port allows MaxScale to connect even when max_connections on the backend server has been reached. Extra-port connections have their own connection limit, which is one by default. This needs to be increased to allow both monitor and user account manager to connect.

If the connection to the extra-port fails due to connection number limit or if the port is not open on the server, normal port is used.

For more information, see extra_port and extra_max_connections.


  • Type: integer
  • Default: 0
  • Dynamic: Yes

Sets the size of the server connection pool. Disabled by default. When enabled, MaxScale places unused connections to the server to a pool and reuses them later. Connections typically become unused when a session closes. If the size of the pool reaches persistpoolmax, unused connections are closed instead.

Every routing thread has its own pool. As of version 6.3.0, MaxScale will round up persistpoolmax so that every thread has an equal size pool.

When a MariaDB-protocol connection is taken from the pool to be used in a new session, the state of the connection is dependent on the router. ReadWriteSplit restores the connection to match the session state. Other routers do not.


The persistmaxtime parameter defaults to zero but can be set to a duration as documented here. If no explicit unit is provided, the value is interpreted as seconds in MaxScale 2.4. In subsequent versions a value without a unit may be rejected. Note that since the granularity of the parameter is seconds, a value specified in milliseconds will be rejected, even if the duration is longer than a second.

A DCB placed in the persistent pool for a server will only be reused if the elapsed time since it joined the pool is less than the given value. Otherwise, the DCB will be discarded and the connection closed.


Maximum number of routing connections to this server. Connections held in a pool also count towards this maximum. Does not limit monitor connections or user account fetching. A value of 0 (default) means no limit.

Since every client session can generate a connection to a server, the server may run out of memory when the number of clients is high enough. This setting limits server memory use caused by MaxScale. The effect depends on if the service setting idle_session_pool_time, i.e. connection sharing, is enabled or not.

If connection sharing is not on, max_routing_connections simply sets a limit. Any sessions attempting to exceed this limit will fail to connect to the backend. The client can still connect to MaxScale, but queries will fail.

If connection sharing is on, sessions exceeding the limit will be put on hold until a connection is available. Such sessions will appear unresponsive, as queries will hang, possibly for a long time. The timeout is controlled by multiplex_timeout.



  • Type: boolean
  • Default: false
  • Dynamic: Yes

If proxy_protocol is enabled, MaxScale will send a PROXY protocol header when connecting client sessions to the server. The header contains the original client IP address and port, as seen by MaxScale. The server will then read the header and perform authentication as if the connection originated from this address instead of MaxScale's IP address. With this feature, the user accounts on the backend server can be simplified to only contain the actual client hosts and not the MaxScale host.

PROXY protocol will be supported by MariaDB 10.3, which this feature has been tested with. To use it, enable the PROXY protocol in MaxScale for every compatible server and configure the MariaDB servers themselves to accept the protocol headers from MaxScale's IP address. On the server side, the protocol should be enabled only for trusted IPs, as it allows the sender to spoof the connection origin. If a proxy header is sent to a server not expecting it, the connection will fail. Usually PROXY protocol should be enabled for every server in a cluster, as they typically have similar grants.

Other SQL-servers may support PROXY protocol as well, but the implementation may be highly restricting. Strict adherence to the protocol requires that the backend server does not allow mixing of un-proxied and proxied connections from a given IP. MaxScale requires normal connections to backends for monitoring and authentication data queries, which would be blocked. To bypass this restriction, the server monitor needs to be disabled and the service listener needs to be configured to disregard authentication errors (skip_authentication=true). Server states also need to be set manually in MaxCtrl. These steps are not required for MariaDB 10.3, since its implementation is more flexible and allows both PROXY-headered and headerless connections from a proxy-enabled IP.


This parameter specifies how full a disk may be, before MaxScale should start logging warnings or take other actions (e.g. perform a switchover). This functionality will only work with MariaDB server versions 10.1.32, 10.2.14 and 10.3.6 onwards, if the DISKS information schema plugin has been installed.

NOTE: Since MariaDB 10.4.7, MariaDB 10.3.17 and MariaDB 10.2.26, the information will be available only if the monitor user has the FILE privilege.

A limit is specified as a path followed by a colon and a percentage specifying how full the corresponding disk may be, before action is taken. E.g. an entry like


specifies that the disk that has been mounted on /data may be used until 80% of the total space has been consumed. Multiple entries can be specified by separating them by a comma. If the path is specified using *, then the limit applies to all disks. However, the value of * is only applied if there is not an exact match.

Note that if a particular disk has been mounted on several paths, only one path need to be specified. If several are specified, then the one with the smallest percentage will be applied.



The last line means that the disk mounted at /data1 may be used up to 80%, the disk mounted at /data2 may be used up to 60% and all other disks mounted at any paths may be used up until 90% of maximum capacity, before MaxScale starts to warn to take action.

Note that the path to be used, is one of the paths returned by:

> use information_schema;
> select * from disks;
| Disk      | Path                 | Total     | Used     | Available |
| /dev/sda3 | /                    |  47929956 | 34332348 |  11139820 |
| /dev/sdb1 | /data                | 961301832 |    83764 | 912363644 |

There is no default value, but this parameter must be explicitly specified if the disk space situation should be monitored.


This parameter controls the order in which servers are used. Valid values for this parameter are primary and secondary. The default value is primary.

This behavior depends on the router implementation but the general rule of thumb is that primary servers will be used before secondary servers.

Readconnroute will always use primary servers before secondary servers as long as they match the configured server type.

Readwritesplit will pick servers that have the same rank as the current primary. Read the readwritesplit documentation on server ranks for a detailed description of the behavior.

The following example server configuration demonstrates how rank can be used to exclude DR-site servers from routing.





The main-site-primary and main-site-replica servers will be used as long as they are available. When they are no longer available, the DR-site-primary and DR-site-replica will be used.


  • Type: integer
  • Default: 0
  • Dynamic: Yes

Server priority. Currently only used by galeramon to choose the order in which nodes are selected as the current primary server. Refer to the Server Priorities section of the galeramon documentation for more information on how to use it.

Starting with MaxScale 2.5.21, this parameter also accepts negative values. In older versions, the parameter only accepted non-negative values.


  • Type: string
  • Default: None
  • Dynamic: Yes

Server-specific custom string added to "CHANGE MASTER TO"-commands sent by MariaDB Monitor. Overrides replication_custom_options setting set in the monitor. This setting affects the server where the command is ran at, not the source of the replication. That is, if monitor sends a "CHANGE MASTER TO"- command to server A telling it to replicate from server B, the setting value from MaxScale configuration for server A would be used.

See MariaDB Monitor documentation for more information.


Monitor sections are used to define the monitoring module that watches a set of servers. Each server can only be monitored by one monitor.

Common monitor parameters can be found here.


A listener defines a port MaxScale listens on for incoming connections. Accepted connections are linked with a MaxScale service. Multiple listeners can feed the same service. Mandatory parameters are type, service and protocol. address is optional, it limits connections to a certain network interface only. socket is also optional and is used for Unix socket connections.

The network socket where the listener listens may have a backlog of connections. The size of this backlog is controlled by the net.ipv4.tcp_max_syn_backlog and net.core.somaxconn kernel parameters.

Increasing the size of the backlog by modifying the kernel parameters helps with sudden connection spikes and rejected connections. For more information see listen(2).



The service to which the listener is associated. This is the name of a service that is defined elsewhere in the configuration file.


The name of the protocol module used for communication between the client and MaxScale. The same protocol is also used for backend communication. Usually this is set to "mariadb". Other allowed values are "postgresql" and "nosqlprotocol".


This sets the address the listening socket is bound to. The address may be specified as an IP address in 'dot notation' or as a hostname. If left undefined the listener will bind to all network interfaces.


The port the listener listens on. If left undefined a default port for the protocol is used.


If defined, the listener uses Unix domain sockets to listen for incoming connections. The parameter value is the name of the socket to use.

If you want to use both network ports and UNIX domain sockets with a service, define two separate listeners that connect to the same service.


The authenticator module to use. Each protocol module defines a default authentication module, which is used if the setting is left undefined. MariaDB and PostgreSQL protocols support multiple authenticators and they can be used simultaneously by giving a comma-separated list e.g. authenticator=PAMAuth,mariadbauth,gssapiauth


Defines additional options for authentication. The value should be a comma-separated list of key-value pairs. See protocol and authenticator specific documentation for more details.


Specify the sql mode for the listener similarly to global sql_mode setting. If both are used this setting will override the global setting for this listener.


Define an IP-address or a subnetwork which may send a proxy protocol header when connecting. The proxy header contains the original client IP-address and port, and MaxScale will use that information in its internal bookkeeping. This means the client is authenticated as if it was connecting from the host in the proxy header. If proxy protocol is also enabled in MaxScale server settings, MaxScale will relay the original original client address and port to the server. See server settings for more information.

This setting may be useful if a compatible load balancer is relaying client connections to MaxScale. If proxy headers are used, both MaxScale and the backends will know where the client originally came from.

The proxy_protocol_networks-setting works similarly to the equivalent setting in MariaDB Server. The value can be a single IP or subnetwork, or a comma-separated list of them. Subnetworks are given in CIDR-format, e.g. "". "*" is a valid value, allowing anyone to send the header. "localhost" allows proxy headers from domain socket connections.

Only trusted IPs should be added to the list, as the proxy header may affect authentication results.


Similar to MariaDB Server, MaxScale will also accept normal connections even if proxy_protocol_networks is configured for the listener.


Path to a text file with sql queries. Any sessions created from the listener will send the contents of the file to backends after authentication. Each non-empty line in the file is interpreted as a query. Each query must succeed for the backend connection to be usable for client queries. The queries should not return any data.


Example query file:

set @myvar = 'mytext';
set @myvar2 = 4;


Path to a json-text file with user and group mapping, as well as server credentials. Only affects MariaDB-protocol based listeners. Default value is empty, which disables the feature.


Should not be used together with PAM Authenticator settings pam_backend_mapping or pam_mapped_pw_file, as these may overwrite the mapped credentials. Is most powerful when combined with service setting user_accounts_file, as then MaxScale can accept users that do not exist on backends and map them to backend users.

This file functions very similar to PAM-based mapping. Both user-to-user and group-to-user mappings can be defined. Also, the password and authentication plugin for the mapped users can be added. The file is only read during listener creation (typically MaxScale start) or when a listener is modified during runtime. When a client logs into MaxScale, their username is searched from the mapping data. If the name matches either a name mapping or a Linux group mapping, the username is replaced by the mapped name. The mapped name is then used when logging into backends. If the file also contains credentials for the mapped user, then those are used. Otherwise, MaxScale tries to log in with an empty password and default MariaDB authentication.

Three arrays are read from the file: user_map, group_map and server_credentials, none of which are mandatory.

Each array element in the user_map-array must define the following fields:

  • original_user: String. Incoming client username.
  • mapped_user: String. Username the client is mapped to.

Each array element in the group_map-array must define the following fields:

  • original_group: String. Incoming client Linux group.
  • mapped_user: String. Username the client is mapped to.

Each array element in the server_credentials-array can define the following fields:

  • mapped_user: String. The mapped username this password is for.
  • password: String. Backend server password. Can be encrypted with maxpasswd.
  • plugin: String, optional. Authentication plugin to use. Must be enabled on the listener. Defaults to empty, which results in standard MariaDB authentication.

When a client successfully logs into MaxScale, MaxScale first searches for name-based mapping. The incoming client does not need to be a Linux user for name-based mapping to take place. If the name is not found, MaxScale checks if the client is a Linux user with a group membership matching an element in the group mapping array. If the client is a member of more than 100 groups, this check may fail.

If a mapping is found, MaxScale searches the credentials array for a matching username, and uses the password and plugin listed. The plugin need not be the same as the one the original user used. Currently, "mysql_native_password" and "pam" are supported as mapped plugins.

An example mapping file is below.

    "user_map": [
            "original_user": "bob",
            "mapped_user": "janet"
            "original_user": "karen",
            "mapped_user": "janet"
    "group_map": [
            "original_group": "visitors",
            "mapped_user": "db_user"
    "server_credentials": [
            "mapped_user": "janet",
            "password": "secret_pw",
            "plugin": "mysql_native_password"
            "mapped_user": "db_user",
            "password": "secret_pw2",
            "plugin": "pam"


  • Type: stringlist
  • Default: character_set_client=auto,character_set_connection=auto,character_set_results=auto,max_allowed_packet=auto,system_time_zone=auto,time_zone=auto,tx_isolation=auto,maxscale=auto
  • Dynamic: Yes
  • Mandatory: No

Metadata that's sent to all connecting clients. The value must be a comma-separated list of key-value arguments. The keys or values cannot contain commas in them.

Any values that are set to auto will be substituted with the value of the corresponding MariaDB system variable. Any system variables that do not not exist or have empty or null values will not be sent to the client. The system variable values are read from the first Master server that's reachable from the listener's service. If no Master server is reachable, the value is read from the first Slave server and if no Slave servers are available, from the first Running server. If no running servers are available, the system variables are not sent.

The exception to this is the maxscale=auto value where the auto will be replaced with the MaxScale version string. This is useful for detecting whether a client is connected to MaxScale. To make MaxScale completely transparent to the client application, the maxscale=auto value can be removed from connection_metadata.

MaxScale will always send a metadata value for threads_connected that contains the current number of connections to the service that the listener points to and for connection_id that contains the 64-bit connection ID value. The values can be overridden by defining them with some value, for example, connection_metadata=threads_connected=0,connection_id=0.

The metadata is implemented using the session state information that is embedded in the OK packets that are generated by MaxScale. The values are encoded as system variables changes. This information can be accessed by all connectors that support reading the session state information. One example of this is the MariaDB Connector/C that implements it with the mysql_session_track_get_first and mysql_session_track_get_next functions.

The following example demonstrates the use of connection_metadata:


The configuration has three variables, redirect_url, service_name and max_allowed_packet that have the values localhost:3306, my-service and auto. The auto value is special and gets replaced with the max_allowed_packet value from the MariaDB server. This means that the final metadata that is sent to the client would be redirect_url=localhost:3306, service_name=my-service and max_allowed_packet=16777216.

Version-specific Behavior

If the connection_metadata variable list contains the tx_isolation variable and the backend MariaDB server from which the variable is retrieved is MariaDB 11 or newer, the value is renamed to transaction_isolation. The tx_isolation parameter was deprecated in favor of transaction_isolation in MariaDB 11 (MDEV-21921).


An include section defined common parameters used in other configuration sections. Consider the following configuration.

backend_connect_timeout = 3s
backend_connect_attempts = 5
servers=Server1, Server2

backend_connect_timeout = 3s
backend_connect_attempts = 5
servers=Server3, Server4

The two monitor sections are identical except for the servers setting. If they otherwise should remain identical, a change must be made in two places. With an include section the situation can be simplified.

backend_connect_timeout = 3s
backend_connect_attempts = 5

servers=Server1, Server2

servers=Server3, Server3

With an include section, all common settings can be defined in one place, and then included to any number of other sections using the @include parameter.

The @include parameter takes a list of section names, so the settings can be distributed across several include sections.

@include=Some-Common-Attributes, Other-Common-Attributes

It is permissible to specify in the including section, parameters that have already been specified in the included section and they will take precedence. For instance, if Monitor2 in the example above should have a longer backend connect timeout it can be specified as follows.

servers=Server3, Server3
backend_connect_timeout = 5s

Note that an included section must be an include section and that an include section cannot include another include section. For instance, both of the following sections would cause an error at startup.



Note also that if an included parameter is changed using maxctrl, it will be changed only on the actual object the change is applied on, not on the include section where the parameter is originally specified.

Available Protocols

Protocol modules in MaxScale define what kind of clients can connect to a listener and what type of backend servers are supported. Protocol is defined in listener settings, and affects both the listener and any services the listener is linked to.

MariaDB or MariaDBClient

Implements MariaDB protocol. The listener will accept MariaDB/MySQL connections from clients and route the client queries through a linked MaxScale service to backend servers. The backends used by the service should be MariaDB servers or compatible.


See Change Data Capture Protocol for more information.

Postgresql or Postgresprotocol

Implements Postgresql protocol. The listener will accept Postgresql connections from clients and route the client queries through a linked MaxScale service to backend servers. The backends used by the service should be PostgreSQL servers or compatible.


Accepts MongoDB® connections, yet stores and fetches results to/from MariaDB servers. See NoSQL documentation for more information.

TLS/SSL encryption

This section describes configuration parameters for both servers and listeners that control the TLS/SSL encryption method and the various certificate files involved in it.

To enable TLS/SSL for a listener, you must set the ssl parameter to true and provide at least the ssl_cert and ssl_key parameters.

To enable TLS/SSL for a server, you must set the ssl parameter to true. If the backend database server has certificate verification enabled, the ssl_cert and ssl_key parameters must also be defined.

Custom CA certificates can be defined with the ssl_ca parameter.

After this, MaxScale connections between the server and/or the client will be encrypted. Note that the database must also be configured to use TLS/SSL connections if backend connection encryption is used.

Note: MaxScale does not allow mixed use of TLS/SSL and normal connections on the same port.

If TLS encryption is enabled for a listener, any unencrypted connections to it will be rejected. MaxScale does this to improve security by preventing accidental creation of unencrypted connections.

The separation of secure and insecure connections differs from the MariaDB server which allows both secure and insecure connections on the same port. As MaxScale is the gateway through which all connections go, in order to guarantee a more secure system MaxScale enforces a stricter security policy than what the server does.

TLS encryption must be enabled for listeners when they are created. For servers, the TLS can be enabled after creation but it cannot be disabled or altered.

Starting with MaxScale 2.5.20, if the TLS certificate given to MaxScale has the X509v3 extended key usage information, MaxScale will check it and refuse to use a certificate with the wrong usage. This means that a certificate with only clientAuth can only be used with servers and a certificate with only serverAuth can only be used with listeners. In order to use the same certificate for both listeners and servers, it must have both the clientAuth and serverAuth usages.


  • Type: boolean
  • Default: false
  • Dynamic: Yes

This enables SSL connections when set to true. The legacy values required and disabled were removed in MaxScale 6.0.

If enabled, the certificate files mentioned above must also be supplied. MaxScale connections to will then be encrypted with TLS/SSL.


A string giving a file path that identifies an existing readable file. The file must be the SSL client private key MaxScale should use. This is a required parameter for listeners but an optional parameter for servers.


A string giving a file path that identifies an existing readable file. The file must be the SSL client certificate MaxScale should use with the server. The certificate must match the key defined in ssl_key. This is a required parameter for listeners but an optional parameter for servers.


Deprecated since MariaDB MaxScale 22.08. See ssl_ca.


A string giving a file path that identifies an existing readable file. The file must be the Certificate Authority (CA) certificate for the CA that signed the certificate referred to in the previous parameter. It will be used to verify that the certificate is valid. This is a required parameter for both listeners and servers. The CA certificate can consist of a certificate chain.

NOTE Up until MariaDB MaxScale 6, the parameter was called ssl_ca_cert, which is still accepted as an alias for ssl_ca.


  • Type: enum_mask
  • Mandatory: No
  • Dynamic: No
  • Values: MAX, TLSv1.0, TLSv1.1, TLSv1.2, TLSv1.3, TLSv10, TLSv11, TLSv12, TLSv13
  • Default: MAX

This parameter controls the allowed TLS version. Accepted values are:

  • TLSv10
  • TLSv11
  • TLSv12
  • TLSv13 (not supported on OpenSSL 1.0)
  • MAX

MaxScale versions 6.4.16, 22.08.13, 23.02.10, 23.08.6, 24.02.2 and all newer releases accept also the following alias values:

  • TLSv1.0
  • TLSv1.1
  • TLSv1.2
  • TLSv1.3 (not supported on OpenSSL 1.0)

The default setting (MAX) allows all supported versions. MaxScale supports TLSv1.0, TLSv1.1, TLSv1.2 and TLSv1.3 depending on the OpenSSL library version. TLSv1.0 and TLSv1.1 are considered deprecated and should not be used, so setting ssl_version=TLSv1.2,TLSv1.3 or ssl_version=TLSv1.3 is recommended.

In MaxScale versions 6.4.13, 22.08.11, 23.02.7, 23.08.3 and earlier, this setting defined the only allowed TLS version, e.g. ssl_version=TLSv12 would only enable TLSv12. The interpretation changed in MaxScale versions 6.4.14, 22.08.12, 23.02.8, 23.08.4 to enable the user to disable old versions while allowing multiple recent TLS versions. In these versions, ssl_version=TLSv1.2 enabled both TLSv1.2 and TLSv1.3.

The interpretation changed again in MaxScale versions 6.4.16, 22.08.13, 23.02.10, 23.08.6, 24.02.2. In these versions the value of ssl_version is an enumeration of accepted TLS protocol versions. This means that admin_ssl_version=TLSv1.2 again only allows TLSv1.2. To retain the behavior from the previous releases where the newer versions were automatically enabled, the protocol versions must be explicitly listed, for example admin_ssl_version=TLSv1.2,TLSv1.3. The change was done to make the ssl_version behave identically to how the MariaDB tls_version parameter works.


Set the list of TLS ciphers. By default, no explicit ciphers are defined and the system defaults are used. Note that this parameter does not modify TLSv1.3 ciphers.


The maximum length of the certificate authority chain that will be accepted. The default value is 9, same as the OpenSSL default. The configured value must be larger than 0.


Peer certificate verification. This functionality is disabled by default. In versions prior to 2.3.17 the feature was enabled by default.

When this feature is enabled, the peer must send a certificate. The certificate sent by the peer is verified against the configured Certificate Authority to make sure the peer is who they claim to be. For listeners, this behaves as if REQUIRE X509 was defined for all users. For servers, this behaves like the --ssl-verify-server-cert command line option for the mysql client.


  • Type: boolean
  • Default: false
  • Dynamic: Yes

Peer host verification.

When this feature is enabled, the peer hostname or IP is verified against the certificate that is sent by the peer. If the IP address or the hostname does not match the one in the certificate returned by the peer, the connection will be closed. If the peer does not provide a certificate, the host verification is not done. To require peer certificates, use ssl_verify_peer_certificate.


A string giving a file path that identifies an existing readable file. The file must be a Certificate Revocation List in the PEM format that defines the revoked certificates. This parameter is only accepted by listeners.

Example SSL enabled server configuration


This example configuration requires all connections to this server to be encrypted with SSL. The paths to the certificate files and the Certificate Authority file are also provided.

Example SSL enabled listener configuration


This example configuration requires all connections to be encrypted with SSL. The paths to the certificate files and the Certificate Authority file are also provided.

Module Types

Routing Modules

The main task of MariaDB MaxScale is to accept database connections from client applications and route the connections or the statements sent over those connections to the various services supported by MariaDB MaxScale.

Currently a number of routing modules are available, these are designed for a range of different needs.

Connection based load balancing: * ReadConnRoute

Read/Write aware statement based router: * ReadWriteSplit

Simple sharding on database level: * SchemaRouter

Binary log server: * Binlogrouter

Monitor Modules

Monitor modules are used by MariaDB MaxScale to internally monitor the state of the backend databases in order to set the server flags for each of those servers. The router modules then use these flags to determine if the particular server is a suitable destination for routing connections for particular query classifications. The monitors are run within separate threads of MariaDB MaxScale and do not affect MariaDB MaxScale's routing performance.

The use of monitors in MaxScale is not absolutely mandatory: it is possible to run MariaDB MaxScale without a monitor module. In this case an external monitoring system must the status of each server via MaxCtrl or the REST API. Only do this if you know what you are doing.

Filter Modules

Filters provide a means to manipulate or process requests as they pass through MariaDB MaxScale between the client side protocol and the query router. A full explanation of each filter's functionality can be found in its documentation.

The Filter Tutorial document shows how you can add a filter to a service and combine multiple filters in one service.

Encrypting Passwords

Passwords stored in the maxscale.cnf file may optionally be encrypted for added security. This is done by creation of an encryption key on installation of MariaDB MaxScale. Encryption keys may be created manually by executing the maxkeys utility with the argument of the filename to store the key. The default location MariaDB MaxScale stores the keys is /var/lib/maxscale. The passwords are encrypted using 256-bit AES CBC encryption.

 # Usage: maxkeys [PATH]
maxkeys /var/lib/maxscale/

Changing the encryption key for MariaDB MaxScale will invalidate any currently encrypted keys stored in the maxscale.cnf file.

Note: The password encryption format changed in MaxScale 2.5. All encrypted passwords created with MaxScale 2.4 or older need to be re-encrypted.

Creating Encrypted Passwords

Encrypted passwords are created by executing the maxpasswd command with the location of the .secrets file and the password you require to encrypt as an argument.

# Usage: maxpasswd PATH PASSWORD
maxpasswd /var/lib/maxscale/ MaxScalePw001

The output of the maxpasswd command is a hexadecimal string, this should be inserted into the maxscale.cnf file in place of the ordinary, plain text, password. MariaDB MaxScale will determine this as an encrypted password and automatically decrypt it before sending it the database server.


Runtime Configuration Changes

Read the following documents for different methods of altering the MaxScale configuration at runtime.

All changes to the configuration done via MaxCtrl are persisted as individual configuration files in /var/lib/maxscale/maxscale.cnf.d/. The content of these files will override any configurations found in the main configuration file or any auxiliary configuration files.

Refer to the Dynamic Configuration section for more details on how this mechanism works and how to disable it.

Configuration Synchronization

The configuration synchronization mechanism is intended for synchronizing configuration changes done on one MaxScale to all other MaxScales. This is done by propagating the changes via the database cluster used by Maxscale.

When configuring configuration synchronization for the first time, the same static configuration files should be used on all MaxScale instances that use the same cluster: the value of config_sync_cluster must be the same on all MaxScale instances and the cluster (i.e. the monitor) pointed by it and its servers must be the same in every configuration.

Whenever the MaxScale configuration is modified at runtime, the latest configuration is stored in the database cluster in the mysql.maxscale_config table. The table is created when the first modification to the configuration is done. A local copy of the configuration is stored in the data directory to allow MaxScale to function even if a connection to the cluster cannot be made. By default this file is stored at /var/lib/maxscale/maxscale-config.json.

Whenever MaxScale starts up, it checks if a local version of this configuration exists. If it does and it is a valid cached configuration, the static configuration file as well as any other generated configuration files are ignored. The exception is the [maxscale] section of the main static configuration file which is always read.

Each configuration has a version number with the initial configuration being version 0. Each time the configuration is modified, the version number is incremented. This version number is used to detect when MaxScale needs to update its configuration.

Error Handling in Configuration Synchronization

When doing a configuration change on the local MaxScale, if the configuration change completes on MaxScale but fails to be committed to the database, MaxScale will attempt to revert the local configuration change. If this attempt fails, MaxScale will discard the cached configuration and abort the process.

When synchronizing with the cluster, if MaxScale fails to apply a configuration retrieved from the cluster, it attempts to revert the configuration to the previous version. If successful, the failed configuration update is ignored. If the configuration update that fails cannot be reverted, the MaxScale configuration will be in an indeterminate state. When this happens, MaxScale will discard the cached configuration and abort the process.

When loading a locally cached configuration during startup, if any errors are found in the cached configuration, it is discarded and the MaxScale process will attempt to restart by exiting with code 75 from the main process. If MaxScale is being used as a SystemD service, this will automatically trigger a restart of MaxScale and no further actions are needed.

The most common reason for a failed configuration update is missing files. For example, if a configuration update adds encrypted connections to a server and the TLS certificates it uses were not copied over to all MaxScale nodes before the change was done, the operation will fail on all nodes that do not have these files.

If the synchronization of the configuration change fails at the step when the database transaction is being committed, the new configuration can be momentarily visible to the local MaxScale. This means the changes are not guaranteed to be atomic on the local MaxScale but are atomic from the cluster's point of view.

Synchronization of Encrypted Passwords

Starting with MaxScale 6.4.9, any passwords that are transmitted by the configuration synchronization are encrypted if password encryption has been enabled in MaxScale. This means that all MaxScale nodes in the same configuration cluster must be configured to use password encryption and they need to all use the same encryption keys that were created with maxkeys.

Managing Configuration Synchronization

The output of maxctrl show maxscale contains the Config Sync field with information about the current configuration state of the local Maxscale as well as the state of any other nodes using this cluster.

│ Config Sync  │ {                                                           │
│              │     "checksum": "3dd6b467760d1d2023f2bc3871a60dd903a3341e", │
│              │     "nodes": {                                              │
│              │         "maxscale": "OK",                                   │
│              │         "maxscale2": "OK"                                   │
│              │     },                                                      │
│              │     "origin": "maxscale",                                   │
│              │     "status": "OK",                                         │
│              │     "version": 2                                            │
│              │ }                                                           │

The version field is the logical configuration version and the origin is the node that originates the latest configuration change. The checksum field is the checksum of the logical configuration and can be used to compare whether two Maxscale instances are in the same configuration state. The nodes field contains the status of each MaxScale instance mapped to the hostname of the server. This field is updated whenever MaxScale reads the configuration from the cluster and can thus be used to detect which MaxScales have updated their configuration.

The mysql.maxscale_config table where the configuration changes are stored must not be modified manually. The only case when the table should be modified is when resetting the configuration synchronization.

To reset the configuration synchronization:

  1. Stop all MaxScale instances
  2. Remove the cached configuration file stored at /var/lib/maxscale/maxscale-config.json on all MaxScale instances
  3. Drop the mysql.maxscale_config table
  4. Start all MaxScale instances

To disable configuration synchronization, remove config_sync_cluster from the configuration file or set it to an empty string: config_sync_cluster="". This can be done at runtime with MaxCtrl by passing an empty string to config_sync_cluster:

maxctrl alter maxscale config_sync_cluster ""

If MaxScale cannot create a connection to the database cluster, configuration changes are not possible until communication with the database is possible. To override this behavior and force the changes to be done, use the --skip-sync option for maxctrl or the sync=false HTTP parameter for the REST API. Any updates done with --skip-sync will overwritten by changes coming from the cluster.

Limitations in Configuration Synchronization

Only the MaxScale configuration is synchronized. Any external files (TLS certificates, configuration files for modules or data generated by MaxScale) are not synchronized. For example, the rule files for the cache filter must be synchronized separately if the filter itself is modified.

Starting with MaxScale 22.08, the Maintenance and Draining states of servers and modifications to the administrative users will be synchronized. In older versions servers had to be put into maintenance mode and users had to be modified separately on each MaxScale.

  • (MXS-3619) External files are not synchronized.

  • (MXS-4276) The --export-config option will not export the cluster configuration and instead exports only the static configuration files. To start a new MaxScale based off of a clustered configuration, copy the static configuration files as well as the JSON configuration in /var/lib/maxscale/maxscale-config.json to the new MaxScale instance.

Backing Up Configuration Changes

The combination of configuration files can be done either manually (e.g. rsync) or with the maxscale --export-config=FILE command line option. See maxscale --help for more information about how to use the --export-config flag.

For example, to export the current runtime configuration, run the following command.

maxscale --export-config=/tmp/maxscale.cnf.combined

This will create the /tmp/maxscale.cnf.combined file and write the current configuration into the it. This allows new MaxScale instances to be easily set up without requiring copying of all runtime configuration files. The user executing the command must be able to read all MaxScale configuration files as well as create and write the provided filename.

Encryption Key Managers

The encryption key managers are how MaxScale retrieves symmetric encryption keys from a key management system. Some parts of MaxScale require the key_manager to be configured in order to work. The key manager that is used is selected with the key_manager parameter and the key manager itself is configured by placing the parameters in the [maxscale] section.

The encryption key managers can be enabled at runtime using maxctrl alter maxscale but cannot be disabled once enabled. To disable the encryption key management, stop Maxscale, remove any persisted configuration files and remove key_manager as well as any key manager options from the static configuration files.

File-based Key Manager

The encryption keys are stored in a text file stored on a local filesystem.

The file uses the same format as the MariaDB server File Key Management Encryption Plugin: a file consisting of an encryption key ID number and the hex-encoded encryption key separated by a semicolon. Read Creating the Key File for more details on how to create the file.

For example, to configure encryption for the nosqlprotocol shared credentials using the file-based encryption key:

  1. Create the key file with (echo -n '1;' ; openssl rand -hex 32) | cat > /var/lib/maxscale/encryption.key

  2. Give MaxScale read permissions on it with chown maxscale:maxscale /var/lib/maxscale/encryption.key

  3. Configure MaxScale with the following:



# Add services, servers, monitors etc.
  1. Start MaxScale


  • Key versioning is not supported



  • Type: path
  • Mandatory: Yes
  • Dynamic: Yes

Path to the file that contains the encryption keys. The user MaxScale runs as (almost always maxscale) must be able to read this file. Encryption keys are read from disk only during startup or when any global MaxScale parameter is modified at runtime.

KMIP Key Manager

Encryption keys are read from a KMIP server.

The KMIP key manager has been verified to work with the PyKMIP server.


  • Key versioning is not supported

  • Encryption keys are not cached locally: whenever MaxScale needs an encryption key, it retrieves it from the KMIP server.


  • Type: string
  • Mandatory: Yes
  • Dynamic: Yes

The host where the KMIP server is.


  • Type: integer
  • Mandatory: Yes
  • Dynamic: Yes

The port on which the KMIP server listens on.


  • Type: path
  • Mandatory: Yes
  • Dynamic: Yes

The client public certificate used when connecting to the KMIP server.


  • Type: path
  • Mandatory: Yes
  • Dynamic: Yes

The client private key used when connecting to the KMIP server.

  • Type: path
  • Default: ""
  • Dynamic: Yes

The CA certificate to use. By default the system default certificates are used.

HashiCorp Vault Key Manager

Encryption keys are read from a local or remote Vault server using the secret engine included in the Vault. This key manager supports versioned keys. Only version 2 key-value stores are supported.

The encryption keys use the same format as the MariaDB HashiCorp Vault Key Management Plugin: The key-value secret for each encryption key ID must contain the field data which must contain a hex-encoded string that is either 32, 48 or 64 characters long.

An easy way to generate a correct encryption key is to use the vault and openssl command line clients. The following command creates a 256-bit encryption key using openssl and stores it using the key ID 1:

$ openssl rand -hex 32|vault kv put secret/1 data=-
== Secret Path ==

======= Metadata =======
Key                Value
---                -----
created_time       2022-06-23T06:50:55.29063873Z
custom_metadata    <nil>
deletion_time      n/a
destroyed          false
version            1


  • Encryption keys are not cached locally: whenever MaxScale needs an encryption key, it retrieves it from the Vault server.



  • Type: password
  • Mandatory: Yes
  • Dynamic: Yes

The authentication token used to connect to the Vault server. This can be encrypted using maxpasswd, similar to how other passwords are encrypted.

  • Type: string
  • Default: localhost
  • Dynamic: Yes

The host where the Vault server is.


  • Type: integer
  • Default: 8200
  • Dynamic: Yes

The port on which the Vault server listens on.

  • Type: path
  • Default: ""
  • Dynamic: Yes

The CA certificate to use. By default the system default certificates are used.


  • Type: boolean
  • Default: true
  • Dynamic: Yes

Whether to use encrypted connections (i.e. HTTPS or HTTP) when communicating with the Vault server.


  • Type: string
  • Default: secret
  • Dynamic: Yes

The Key-Value mount where the secret is stored. By default the secret mount is used which is present by default in most Vault installations.


  • Type: duration
  • Default: 30s
  • Dynamic: Yes

The connection and request timeout used with the Vault server.


For routing, MaxScale uses asynchronous I/O and a fixed number of threads (aka routing workers), whose number up until 23.02 was fixed at startup. From 23.02 onwards the number of threads can be altered at runtime, which is convenient, for instance, if MaxScale is running in a container whose properties are changed during the lifetime of the container.

A thread can be in three different states: * Active: The thread is routing client traffic and is listening for new connections. * Draining: The thread is routing client traffic but is not listening for new connections. * Dormant: The thread is not routing client traffic (all sessions have ended), and is not listening for new connections, and is waiting to be terminated.

All threads start as Active and may become Draining if the number of threads is reduced. A draining thread will eventually become Dormant, unless the number of threads is increased while the thread is still Draining.

Note that it is not possible to terminate a specific thread, but it is only possible to specify the number of threads that MaxScale should use, and that the threads will be terminated from the end. This has implications if the number of threads is reduced by more than 1, as a Dormant thread will not be terminated before it is the last thread.

In the following, MaxScale has been started with threads=4.

$ bin/maxctrl show threads
│ Id                     │ 0      │ 1      │ 2      │ 3      │ All │
│ State                  │ Active │ Active │ Active │ Active │ N/A │

All threads are Active. If we now decrease the number of threads

$ bin/maxctrl alter maxscale threads=2
$ bin/maxctrl show threads
│ Id                     │ 0      │ 1      │ 2        │ 3        │ All     │
│ State                  │ Active │ Active │ Draining │ Draining │ N/A     │

we will see that the threads 2 and 3 are now Draining. The reason is that threads 2 and 3 still handle client sessions. If some client sessions now end, the situation may become like

│ Id                     │ 0      │ 1      │ 2       │ 3        │ All    │
│ State                  │ Active │ Active │ Dormant │ Draining │ N/A    │

That is, thread 2 is Dormant and thread 3 is Draining. All client sessions that were handled by thread 2 have ended and the thread is ready to be terminated. However, as thread 3 is still Draining, thread 2 will not be terminated but stay Dormant.

If the sessions handled by thread 3 end, then it will become Dormant at which point first thread 3 will be terminatad and immediately after that thread 2.

$ bin/maxctrl show threads
│ Id                     │ 0      │ 1      │ All  │
│ State                  │ Active │ Active │ N/A  │

If the situation is like

$ bin/maxctrl show threads
│ Id                     │ 0      │ 1      │ 2       │ 3        │ All    │
│ State                  │ Active │ Active │ Dormant │ Draining │ N/A    │

that is, the number of threads was 4 but has been reduced to 2, and while thread 2 has become drained it stays as Dormant since thread 3 is still Draining, it is possible to make thread 2 Active again by increasing the number of threads to 3.

$ bin/maxctrl alter maxscale threads=3
wikman@johan-P53s:maxscale $ bin/maxctrl show threads
│ Id                     │ 0      │ 1      │ 2      │ 3        │ All    │
│ State                  │ Active │ Active │ Active │ Draining │ N/A    │

Once the sessions of thread 3 ends, we will have

$ bin/maxctrl show threads
│ Id                     │ 0      │ 1      │ 2      │ All  │
│ State                  │ Active │ Active │ Active │ N/A  │

Error Reporting

MariaDB MaxScale is designed to be executed as a service, therefore all error reports, including configuration errors, are written to the MariaDB MaxScale error log file. By default, MariaDB MaxScale will log to a file in /var/log/maxscale and the system log.


The current limitations of MaxScale are listed in the Limitations document.

Performance Optimization

  • Tune query_classifier_cache_size to allow maximal use of the query classifier cache. Increase the value and/or system memory until the set of unique SQL patterns fits into memory. By default at most 15% of the system memory is used for this cache. To detect if the SQL statements fit into memory, monitor the QC cache evictions value in maxctrl show threads to see how many evictions take place. If it keeps increasing, increase the size of the query classifier cache. Using the query classifier cache with a CPU bound workload gives a roughly 20% improvement in performance compared to when it is turned off.

  • A faster CPU with more CPU cores is better. This is true for most applications but especially for MaxScale as it is mostly limited by the speed of the CPU. Using threads=auto is recommended (the default starting with MaxScale 6).

  • Network throughput between the client, MaxScale and the database nodes governs how much traffic can be handled. The client-to-MaxScale network is likely to be saturated first: having multiple MaxScales in front of the cluster is an easy way of solving this problem.

  • Certain MaxScale modules store data on disk. A faster disk improves their performance but depending on the module, this might not be a big enough of a problem to worry about. Filters like the qlafilter that write information to disk for every SQL query can cause performance bottlenecks.

MaxScale Diagnostics using MaxCtrl

From 22.08.2 onwards, maxctrl show maxscale shows a System object with information about the system MaxScale is running on. The fields are:

Field Meaning
machine.cores_physical The number of physical CPU cores on the machine.
machine.cores_available The number of CPU cores available to MaxScale. This number may be smaller than machine.cores_physical, if CPU affinities are used and only a subset of the physical cores are available to MaxScale.
machine.cores_virtual The number of virtual CPU cores available to MaxScale. This number may be a decimal and smaller than machine.cores_available, if MaxScale is running in a container whose CPU quota and period has been restricted. Note that if MaxScale is not, or fails to detect it is running in a container, the value shown will be identical with machine.cores_available.
machine.memory_physical The amount of physical memory on the machine.
machine.memory_available The amount of memory available to MaxScale. This number may be smaller than machine.memory_physical, if MaxScale is running in a container whose memory has been restricted. Note that if MaxScale is not, or fails to detect it is running in a container, the value shown will be identical with machine.memory_physical. Note also that the amount is available to all processes running in the same container, not just to MaxScale.
maxscale.query_classifier_cache_size The maximum size of the MaxScale query classifier cache.
maxscale.threads The number of routing threads used by MaxScale.

In addition there is an os object that contains what the Linux command uname displays.



If threads has not been specified at all in the MaxScale configuration file, or if its value is auto, then MaxScale will use as many routing threads as there are physical cores on the machine. This is the right choice, if MaxScale is running on a dedicated machine or in a container that has not been restriced in any way.

However, if the number of cores available to MaxScale have been restricted or if MaxScale is running in a container whose CPU quota and period have been limited, then it will lead to MaxScale using more routing threads than what is appropriate in the environment where it is running.

If machine.cores_virtual is less than machine.cores_physical, then threads should be specified explicitly in the MaxScale configuration file and its value should be that of machine.cores_virtual rounded up to the nearest integer. If that value is 1 it may be beneficial to check whether 2 gives better performance.


If query_classifier_cache_size has not been specified in the MaxScale configuration file, then MaxScale will use at most 15% of the amount of physical memory in the machine for the cache. This is a good starting point, if MaxScale is running on a dedicated machine or in a container that has not been restriced in any way. Note that the amount specifies how much memory the cache at maximum is allowed to use, not what would immediately be allocated for the cache.

However, if the amount of memory available to MaxScale has been restricted, which may be the case if MaxScale is running in a container, this may cause the cache to grow beyond what is available, which will lead to a crash or MaxScale being killed.

If the value of machine.memory_available is less than that of machine.memory_physical, then query_classifier_cache_size should be explicitly set to 15% of maxscale.memory_available. The value can be larger, but must not be a bigger share of machine.memory_available than what is reasonable.


$ maxctrl show maxscale
│ System       │ {                                                                          │
│              │     "machine": {                                                           │
│              │         "cores_available": 8,                                              │
│              │         "cores_physical": 8,                                               │
│              │         "cores_virtual": 4,                                                │
│              │         "memory_available": 20858544128,                                   │
│              │         "memory_physical": 41717088256                                     │
│              │     },                                                                     │
│              │     "maxscale": {                                                          │
│              │         "query_classifier_cache_size": 6257563238,                         │
│              │         "threads": 8                                                       │
│              │     },                                                                     │
│              │     "os": {                                                                │
│              │         "machine": "x86_64",                                               │
│              │         "nodename": "johan-P53s",                                          │
│              │         "release": "5.4.0-125-generic",                                    │
│              │         "sysname": "Linux",                                                │
│              │         "version": "#141~18.04.1-Ubuntu SMP Thu Aug 11 20:15:56 UTC 2022"  │
│              │     }                                                                      │
│              │ }                                                                          │

As can be seen, maxscale.threads is larger than machine.cores_virtual and thus, threads=4 should explicitly be specified in the MaxScale configuration file.

maxscale.query_classifier_cache_size is the default 15% of machine.memory_physical but as machine.memory_available is just half of that, something like query_classifier_cache_size=3100000000 (~15% of machine.memory_available) should be added to the configuration file.



For a list of common problems and their solutions, read the MaxScale Troubleshooting article on the MariaDB Knowledge Base.

Systemd Watchdog

If MaxScale is running as a systemd service, the systemd Watchdog will be enabled by default. To configure it, change the WatchdogSec option in the Service section of the maxscale systemd configuration file located in /lib/systemd/system/maxscale.service:


It is not recommended to use a watchdog timeout less than 30 seconds. When enabled MaxScale will check that all threads are running and notify systemd with a "keep-alive ping".

Systemd reference:


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