MaxScale 21.06 Readconnroute


This document provides an overview of the readconnroute router module and its intended use case scenarios. It also displays all router configuration parameters with their descriptions.


The readconnroute router provides simple and lightweight load balancing across a set of servers. The router can also be configured to balance connections based on a weighting parameter defined in the server's section.

Note that *readconnroute balances connections and not statements. When a client connects, the router selects a server based upon the router configuration and current server load, but the single created connection is fixed and will not be changed for the duration of the session. If the connection between MaxScale and the server breaks, the connection can not be re-established and the session will be closed. The fact that the server is fixed when the client connects also means that routing hints are ignored.

Warning: readconnroute will not prevent writes from being done even if you define router_options=slave. The client application is responsible for making sure that it only performs read-only queries in such cases. readconnroute is simple by design: it selects a server for each client connection and routes all queries there. If something more complex is required, the readwritesplit router is usually the right choice.


For more details about the standard service parameters, refer to the Configuration Guide.


router_options can contain a comma separated list of valid server roles. These roles are used as the valid types of servers the router will form connections to when new sessions are created.



Here is a list of all possible values for the router_options.

Role Description
master A server assigned as a master by one of MariaDB MaxScale monitors. Depending on the monitor implementation, this could be a master server of a Master-Slave replication cluster or a Write-Master of a Galera cluster.
slave A server assigned as a slave of a master. If all slaves are down, but the master is still available, then the router will use the master.
synced A Galera cluster node which is in a synced state with the cluster.
running A server that is up and running. All servers that MariaDB MaxScale can connect to are labeled as running.

If no router_options parameter is configured in the service definition, the router will use the default value of running. This means that it will load balance connections across all running servers defined in the servers parameter of the service.

When a connection is being created and the candidate server is being chosen, the list of servers is processed in from first entry to last. This means that if two servers with equal weight and status are found, the one that's listed first in the servers parameter for the service is chosen.


This option can be used to prevent queries from being sent to the current master. If router_options does not contain "master", the readconnroute instance is usually meant for reading. Setting master_accept_reads=false excludes the master from server selection (and thus from receiving reads).

If router_options contains "master", the setting of master_accept_reads has no effect.

By default master_accept_reads=true.


The maximum acceptable replication lag. The value is in seconds and is specified as documented here. The default value is 0s, which means that the lag is ignored.

The replication lag of a server must be less than the configured value in order for it to be used for routing. To configure the router to not allow any lag, use the smallest duration larger than 0, that is, max_replication_lag=1s.


The most common use for the readconnroute is to provide either a read or write port for an application. This provides a more lightweight routing solution than the more complex readwritesplit router but requires the application to be able to use distinct write and read ports.

To configure a read-only service that tolerates master failures, we first need to add a new section in to the configuration file.


Here the router_options designates slaves as the only valid server type. With this configuration, the queries are load balanced across the slave servers.

For more complex examples of the readconnroute router, take a look at the examples in the Tutorials folder.

Router Diagnostics

The router_diagnostics output for readconnroute has the following fields.

  • queries: Number of queries executed through this service.


  • Sending of binary data with LOAD DATA LOCAL INFILE is not supported.

  • The router will never reconnect to the server it initially connected to.


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