MaxScale 21.06 Named Server Filter

Named Server Filter


The namedserverfilter is a MariaDB MaxScale filter module able to route queries to servers based on regular expression (regex) matches. Since it is a filter instead of a router, the NamedServerFilter only sets routing suggestions. It requires a compatible router to be effective. Currently, both readwritesplit and hintrouter take advantage of routing hints in the data packets. This filter uses the PCRE2 library for regular expression matching.


The filter accepts settings in two modes: legacy and indexed. Only one of the modes may be used for a given filter instance. The legacy mode is meant for backwards compatibility and allows only one regular expression and one server name in the configuration. In indexed mode, up to 25 regex-server pairs are allowed in the form match01 - target01, match02 - target02 and so on. Also, in indexed mode, the server names (targets) may contain a list of names or special tags ->master or ->slave.

All parameters except the deprecated match and target parameters can be modified at runtime. Any modifications to the filter configuration will only affect sessions created after the change has completed.

Below is a configuration example for the filter in indexed-mode. The legacy mode is not recommended and may be removed in a future release. In the example, a SELECT on TableOne (match01) results in routing hints to two named servers, while a SELECT on TableTwo is suggested to be routed to the master server of the service. Whether a list of server names is interpreted as a route-to-any or route-to-all is up to the attached router. The HintRouter sees a list as a suggestion to route-to-any. For additional information on hints and how they can also be embedded into SQL-queries, see Hint-Syntax.



Filter Parameters

NamedServerFilter requires at least one matchXY - targetXY pair.

matchXY, options

matchXY defines a PCRE2 regular expression against which the incoming SQL query is matched. XY must be a number in the range 01 - 25. Each match-setting pairs with a similarly indexed target- setting. If one is defined, the other must be defined as well. If a query matches the pattern, the filter attaches a routing hint defined by the target-setting to the query. The options-parameter affects how the patterns are compiled as usual.



The hint which is attached to the queries matching the regular expression defined by matchXY. If a compatible router is used in the service the query will be routed accordingly. The target can be one of the following:

  • a server or service name (adds a HINT_ROUTE_TO_NAMED_SERVER hint)
  • a list of server names, comma-separated (adds several HINT_ROUTE_TO_NAMED_SERVER hints)
  • ->master (adds a HINT_ROUTE_TO_MASTER hint)
  • ->slave (adds a HINT_ROUTE_TO_SLAVE hint)
  • ->all (adds a HINT_ROUTE_TO_ALL hint)

The support for service names was added in MaxScale 6.3.2. Older versions of MaxScale did not accept service names in the target parameters.



This optional parameter defines an IP address or mask which a connecting client's IP address is matched against. Only sessions whose address matches this setting will have this filter active and performing the regex matching. Traffic from other client IPs is simply left as is and routed straight through.


Since MaxScale 2.1 it's also possible to use % wildcards:


Note that using source=% to match any IP is not allowed.

Since MaxScale 2.3 it's also possible to specify multiple addresses separated by comma. Incoming client connections are subsequently checked against each.



This optional parameter defines a user name the connecting client username is matched against. Only sessions that are connected using this username will have the match and routing hints applied to them. Traffic from users is simply left as is and routed straight through.


Additional remarks

The maximum number of accepted match - target pairs is 25.

In the configuration file, the indexed match and target settings may be in any order and may skip numbers. During SQL-query matching, however, the regexes are tested in ascending order: match01, match02, match03 and so on. As soon as a match is found for a given query, the routing hints are written and the packet is forwarded to the next filter or router. Any remaining match regexes are ignored. This means the match - target pairs should be indexed in priority order, or, if priority is not a factor, in order of decreasing match probability.

Binary-mode prepared statements (COM_STMT_PREPARE) are handled by matching the prepared sql against the match-parameters. If a match is found, the routing hints are attached to any execution of that prepared statement. Text- mode prepared statements are not supported in this way. To divert them, use regular expressions which match the specific "EXECUTE"-query.


Example 1 - Route queries targeting a specific table to a server

This will route all queries matching the regular expression *from *users to the server named server2. The filter will ignore character case in queries.

A query like SELECT * FROM users would be routed to server2 where as a query like SELECT * FROM accounts would be routed according to the normal rules of the router.

match02= *from *users



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