MariaDB MaxScale Configuration Guide

Introduction

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.

Concepts

Glossary

Objects

Server

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.

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

Monitor

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 master-slave 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.

Filter

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 are dbfwfilter that is a configurable firewall, 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.

Router

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.

Service

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.

Listener

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.

Administration

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 provded.

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_cert
• admin_ssl_cert
• admin_ssl_key
• admin_ssl_version
• cachedir
• connector_plugindir
• datadir
• debug
• execdir
• language
• libdir
• load_persisted_configs
• local_address
• log_augmentation
• log_warn_super_user
• logdir
• module_configdir
• persistdir
• piddir
• query_classifier_args
• query_classifier
• query_retries
• secretsdir
• sql_mode
• sharedir
• substitute_variables
• threads

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

Configuration

The MariaDB MaxScale configuration is read from a file that MariaDB MaxScale will look for in the following places:

1. By default, the file maxscale.cnf in the directory /etc
2. The location given with the --configdir=<path> command line argument.

MariaDB MaxScale will further look for a directory with the same name as the configuration file, followed by .d (for instance /etc/maxscale.cnf.d) and recursively read all files, having a .cnf suffix, it finds in the directory hierarchy. All other files will be ignored.

There are no restrictions on how different configuration sections are arranged, but the strong suggestion is to place global settings into the configuration file MariaDB MaxScale is invoked with, and then, if deemed necessary, create separate configuration files for servers, filters, etc.

The configuration file itself is based on the .ini file format and consists of various sections that are used to build the configuration; these sections define services, servers, listeners, monitors and global settings.

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

# This is a comment before a parameter
some_parameter=123

Note: Multi-line parameters have been deprecated in MaxScale 6.0 due to the unintuitive way they worked when the same parameter was declared multiple times.

Parameters, which expect a comma-separated list of values can be defined on multiple lines. The following is an example of a multi-line definition.

[MyService]
type=service
router=readconnroute
servers=server1,
        server2,
        server3

The values of the parameter that are not on the first line need to have at least one whitespace character before them in order for them to be recognized as a part of the multi-line parameter.

Names

Section names may not contain whitespace and must not start with the characters @@, but otherwise there are no restrictions.

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 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

Booleans

Boolean type parameters interpret the values true, yes, on and 1 as true values and false, no, off and 0 as false values. The REST API only accepts JSON boolean values for boolean type parameters.

Sizes

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

max_size=1099511628000
max_size=1073741824Ki
max_size=1048576Mi
max_size=1024Gi
max_size=1Ti

are equivalent, as are the following

max_size=1000000000000
max_size=1000000000k
max_size=1000000M
max_size=1000G
max_size=1T

Durations

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

soft_ttl=1h
soft_ttl=60m
soft_ttl=60min
soft_ttl=3600s
soft_ttl=3600000ms

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.

Enumerations

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:

router_options=master,slave

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.

threads

This parameter controls the number of worker threads that are handling the events coming from the kernel. 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.

The maximum value for threads is 100.

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

[MaxScale]
threads=auto

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.

rebalance_period

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.

rebalance_period=10s

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

NOTE The rebalancing functionality is currently disabled and an attempt to enable it will be ignored.

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.

rebalance_threshold

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.

rebalance_threshold=15

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

rebalance_window

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.

skip_name_resolve

• 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'@'my-hostname.org'), 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.

auth_connect_timeout

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.

auth_connect_timeout=10s

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.

auth_read_timeout

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

auth_write_timeout

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

query_retries

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.

query_retry_timeout

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.

passive

• 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.

ms_timestamp

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

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

skip_permission_checks

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

Skip service and monitor user permission checks. This is useful when you know the permissions are OK and you want to speed up the startup process.

It is recommended to not disable the permission checks so that any missing privileges are detected when maxscale is starting up. If you are experiencing a slow startup of MaxScale due to large amounts of connection timeouts when permissions are checked, disabling the permission checks could speed up the startup process.

skip_permission_checks=true

syslog

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

Log messages to syslog.

maxlog

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

Log messages to MariaDB MaxScale's log file.

log_warning

• 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.

log_notice

• 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.

log_info

• 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.

log_debug

• 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.

log_warn_super_user

• 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 master server switchover. Super-users bypass the read_only-flag which switchover uses to block writes to the master.

log_augmentation

• 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>
log_augmentation=1

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

log_throttling

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

log_throttling=

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.

logdir

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/.

logdir=/var/log/maxscale/

datadir

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/.

datadir=/var/lib/maxscale/

secretsdir

• 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.

libdir

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/

libdir=/usr/lib64/maxscale/

sharedir

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/.

cachedir

Configure the directory MariaDB MaxScale uses to store cached data.

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

cachedir=/var/cache/maxscale/

piddir

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/.

piddir=/var/run/maxscale/

execdir

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/.

execdir=/usr/bin/

connector_plugindir

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.

connector_plugindir=/usr/lib64/maxscale/plugin/

persistdir

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/.

persistdir=/var/lib/maxscale/maxscale.cnf.d/

module_configdir

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 e.g. dbfwfilter rule files.

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/.

module_configdir=/etc/maxscale.modules.d/

language

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/.

language=/var/lib/maxscale/

query_classifier

The module used by MariaDB MaxScale for query classification. The information provided by this module is used by MariaDB MaxScale when deciding where a particular statement should be sent. The default query classifier is qc_sqlite.

query_classifier_cache_size

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
query_classifier_cache_size=1MB

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.

query_classifier_args

Arguments for the query classifier. What arguments are accepted depends on the particular query classifier being used. The default query classifier - qc_sqlite - supports the following arguments:

log_unrecognized_statements

An integer argument taking the following values: * 0: Nothing is logged. This is the default. * 1: Statements that cannot be parsed completely are logged. They may have been partially parsed, or classified based on keyword matching. * 2: Statements that cannot even be partially parsed are logged. They may have been classified based on keyword matching. * 3: Statements that cannot even be classified by keyword matching are logged.

query_classifier=qc_sqlite
query_classifier_args=log_unrecognized_statements=1

This will log all statements that cannot be parsed completely. This may be useful if you suspect that MariaDB MaxScale routes statements to the wrong server (e.g. to a slave instead of to a master).

substitute_variables

• 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

some_parameter=$SOME_VALUE

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.

substitute_variables=true

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.

sql_mode

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.

sql_mode=oracle

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;

and

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.

local_address

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.

local_address=192.168.1.254

users_refresh_time

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.

users_refresh_time=120s

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.

users_refresh_interval

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.

users_refresh_interval=2h

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

retain_last_statements

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.

retain_last_statements=20

Default is 0.

dump_last_statements

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.

dump_last_statements=on_error

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.

session_trace

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.

session_trace=20

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.

session_trace_match

• 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=1000
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.

writeq_high_water

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 16777216 bytes.

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 both writeq_high_water and writeq_low_water have a non-zero value. To disable throttling, set the value to 0.

writeq_low_water

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 8192 bytes.

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

Network throttling is only enabled when both writeq_high_water and writeq_low_water have a non-zero value. To disable throttling, set the value to 0.

load_persisted_configs

• 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.

max_auth_errors_until_block

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.

debug

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.

admin_host

The network interface where the REST API listens on. The default value is the IPv4 address 127.0.0.1 which only listens for local connections.

admin_port

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

admin_auth

• 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.

admin_ssl_key

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.

admin_ssl_cert

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

admin_ssl_ca_cert

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.

admin_ssl_version

• 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

admin_enabled

• 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.

admin_gui

• 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.

admin_secure_gui

• 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.

admin_log_auth_failures

• 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.

config_sync_cluster

• 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.

config_sync_user

• 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,
  nodes JSON NOT NULL
) ENGINE=InnoDB;

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

config_sync_password

• 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.

config_sync_db

• 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.

config_sync_interval

• 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.

config_sync_timeout

• 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.

Events

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:

event.X.facility=LOG_LOCAL0
event.X.level=LOG_ERR

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:

'authentication_failure'

This event occurs when there is an authentication failure.

event.authentication_failure.facility=LOG_AUTH
event.authentication_failure.level=LOG_CRIT

Service

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.

[Test-Service]
type=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.

router

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.

router=readconnroute
router_options=slave

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.

router=readconnroute
router_options=master,slave

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

router_options

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.

filters

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.

targets

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.

targets=My-Service,server2

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.

servers

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).

servers=server1,server2,server3

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

cluster

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

cluster=TheMonitor

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.

user=maxscale
password=Mhu87p2D

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

enable_root_user

• 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.

localhost_match_wildcard_host

Deprecated and ignored.

version_string

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

Example:

version_string=10.11.2-MariaDB-RWsplit

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.

auth_all_servers

• 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.

strip_db_esc

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

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.

log_auth_warnings

• 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.

log_warning

• 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.

log_notice

• 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.

log_info

• 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.

log_debug

• 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.

connection_timeout

The connection_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.

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.

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_timeout for those is not used.

The value of connection_timeout 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 both connection_timeout and wait_timeout. 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.

In MaxScale versions 6.2.0 and older, if long-running operations (e.g. ALTER TABLE) were performed, MaxScale would close the connections if they look longer than connection_timeout seconds to execute (MXS-3893). In MaxScale 6.2.1 this has been fixed and the active operations are now correctly tracked.

Example:

[Test-Service]
connection_timeout=300s

max_connections

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.

Example:

[Test-Service]
max_connections=100

session_track_trx_state

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

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

retain_last_statements

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

connection_keepalive

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.

force_connection_keepalive

• 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.

net_write_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.

max_sescmd_history

• 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.

prune_sescmd_history

• 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.

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.

disable_sescmd_history

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

This option disables the session command history. This way no history is stored and if a slave server fails, the router will not try to replace the failed slave. 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.

user_accounts_file

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

user_accounts_file=/home/root/users.json

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": "127.0.0.1",
            "password": "*032169CDF0B90AF8C00992D43D354E29A2EACB42",
            "plugin": "mysql_native_password",
            "default_role": "role2"
        },
        {
            "user": "",
            "host": "%",
            "plugin": "pam",
            "proxy_priv": true
        }
    ],
    "db": [
        {
            "user": "test2",
            "host": "127.0.0.1",
            "db": "test"
        }
    ],
    "roles_mapping": [
        {
            "user": "test2",
            "host": "127.0.0.1",
            "role": "role2"
        }
    ]
}

user_accounts_file_usage

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.

user_accounts_file_usage=file_only_always

idle_session_pool_time

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 is by default given in seconds, but can also be given in 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.

idle_session_pool_time=900ms

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:

max_slave_connections=1
lazy_connect=1
transaction_replay=true

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

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

[server1]
type=server
max_routing_connections=1000 #this should be based on MariaDB Server capacity
persistpoolmax=1000 #same as above
persistmaxtime=10
#other server settings...

[myservice]
type=service
max_slave_connections=1
transaction_replay=true
idle_session_pool_time=500ms
lazy_connect=1
#other service settings...

multiplex_timeout

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.

multiplex_timeout=33s

Server

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.

[MyMariaDBServer1]
type=server
address=127.0.0.1
port=3000

address

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.

port

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

socket

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.

monitoruser=mymonitoruser
monitorpw=mymonitorpasswd

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

extra_port

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.

persistpoolmax

• 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.

persistmaxtime

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.

max_routing_connections

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.

max_routing_connections=1234

proxy_protocol

• 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.

disk_space_threshold

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

/data:80

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.

Examples:

disk_space_threshold=*:80
disk_space_threshold=/data:80
disk_space_threshold=/data1:80,/data2:60,*:90

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.

rank

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 master. 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.

[main-site-master]
type=server
address=192.168.0.11
rank=primary

[main-site-slave]
type=server
address=192.168.0.12
rank=primary

[DR-site-master]
type=server
address=192.168.0.21
rank=secondary

[DR-site-slave]
type=server
address=192.168.0.22
rank=secondary

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

priority

• 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 master 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.

Monitor

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.

Listener

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).

[MyListener1]
type=listener
service=MyService1
protocol=MariaDBClient
port=3006

service

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

protocol

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 MariaDBClient.

address

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.

port

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

socket

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.

authenticator

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

authenticator_options

This defines additional options for authentication. As of MaxScale 2.5.0, only MariaDBClient and its authenticators support additional options. The value of this parameter should be a comma-separated list of key-value pairs. See authenticator specific documentation for more details.

sql_mode

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.

connection_init_sql_file

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.

connection_init_sql_file=/home/dba/init_queries.txt

Example query file:

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

user_mapping_file

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.

user_mapping_file=/home/root/mapping.json

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"
        }
    ]
}

Available Protocols

The protocols supported by MariaDB MaxScale are implemented as external modules that are loaded dynamically into the MariaDB MaxScale core. They allow MariaDB MaxScale to communicate in various protocols both on the client side and the backend side. Each of the protocols can be either a client protocol or a backend protocol. Client protocols are used for client-MariaDB MaxScale communication and backend protocols are for MariaDB MaxScale-database communication.

MariaDBClient

This is the implementation of the MySQL-protocol. When defined for a listener, the listener will accept MySQL-connections from clients, assign them to a MaxScale service and route the queries from the client to backend servers. Any backends used by the service should be MariaDB/MySQL-servers or compatible.

CDC

See Change Data Capture Protocol 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_cert 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.

ssl

• 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.

ssl_key

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.

ssl_cert

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.

ssl_ca_cert

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.

ssl_version

• 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.

ssl_cipher

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.

ssl_cert_verify_depth

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.

ssl_verify_peer_certificate

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.

ssl_verify_peer_host

• 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.

ssl_crl

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

[server1]
type=server
address=10.131.24.62
port=3306
ssl=true
ssl_cert=/usr/local/mariadb/maxscale/ssl/crt.max-client.pem
ssl_key=/usr/local/mariadb/maxscale/ssl/key.max-client.pem
ssl_ca_cert=/usr/local/mariadb/maxscale/ssl/crt.ca.maxscale.pem

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

[RW-Split-Listener]
type=listener
service=RW-Split-Router
protocol=MariaDBClient
port=3306
ssl=true
ssl_cert=/usr/local/mariadb/maxscale/ssl/crt.maxscale.pem
ssl_key=/usr/local/mariadb/maxscale/ssl/key.csr.maxscale.pem
ssl_ca_cert=/usr/local/mariadb/maxscale/ssl/crt.ca.maxscale.pem

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.

• MariaDB Monitor
• Galera Monitor

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.

• Query Log All (QLA) Filter
• Regular Expression Filter
• Tee Filter
• Top Filter
• Database Firewall Filter
• Query Redirection Filter

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
61DD955512C39A4A8BC4BB1E5F116705

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.

[Split-Service]
type=service
router=readwritesplit
servers=server1,server2,server3,server4
user=maxscale
password=61DD955512C39A4A8BC4BB1E5F116705

Runtime Configuration Changes

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

• MaxCtrl
• create
• destroy
• add
• remove

• alter

• REST API documentation

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

• (MXS-3619) The synchronization only affects the MaxScale configuration. The state of objects or any external files (e.g. TLS certificates) are not synchronized by this mechanism.

• (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.

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.

Limitations

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.

Troubleshooting

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:

WatchdogSec=30s

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: https://www.freedesktop.org/software/systemd/man/systemd.service.html