--- name: "pt-variable-advisor" section: "1p" platform: "linux" package: "percona-toolkit" version: "3.7.1_4-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/pt-variable-advisor" --- # pt-variable-advisor(1p) Analyze MySQL variables and advise on possible problems. ## NAME pt-variable-advisor - Analyze MySQL variables and advise on possible problems. ## SYNOPSIS Usage: pt-variable-advisor \[OPTIONS\] \[DSN\] pt-variable-advisor analyzes variables and advises on possible problems. Get SHOW VARIABLES from localhost: ``` pt-variable-advisor localhost ``` Get SHOW VARIABLES output saved in vars.txt: ``` pt-variable-advisor --source-of-variables vars.txt ``` ## RISKS Percona Toolkit is mature, proven in the real world, and well tested, but all database tools can pose a risk to the system and the database server. Before using this tool, please: - • Read the tool's documentation - • Review the tool's known "BUGS" - • Test the tool on a non-production server - • Backup your production server and verify the backups ## DESCRIPTION pt-variable-advisor examines `"SHOW VARIABLES"` for bad values and settings according to the "RULES" described below. It reports on variables that match the rules, so you can find bad settings in your MySQL server. ## RULES These are the rules that pt-variable-advisor will apply to SHOW VARIABLES. Each rule has three parts: an ID, a severity, and a description. The rule's ID is a short, unique name for the rule. It usually relates to the variable that the rule examines. If a variable is examined by several rules, then the rules' IDs are numbered like "-1", "-2", "-N". The rule's severity is an indication of how important it is that this rule matched a query. We use NOTE, WARN, and CRIT to denote these levels. The rule's description is a textual, human-readable explanation of what it means when a variable matches this rule. Depending on the verbosity of the report you generate, you will see more of the text in the description. By default, you'll see only the first sentence, which is sort of a terse synopsis of the rule's meaning. At a higher verbosity, you'll see subsequent sentences. - auto\_increment severity: note Are you trying to write to more than one server in a dual-source or ring replication configuration? This is potentially very dangerous and in most cases is a serious mistake. Most people's reasons for doing this are actually not valid at all. - concurrent\_insert severity: note Holes (spaces left by deletes) in MyISAM tables might never be reused. - connect\_timeout severity: note A large value of this setting can create a denial of service vulnerability. - debug severity: crit Servers built with debugging capability should not be used in production because of the large performance impact. - delay\_key\_write severity: warn MyISAM index blocks are never flushed until necessary. If there is a server crash, data corruption on MyISAM tables can be much worse than usual. - flush severity: warn This option might decrease performance greatly. - flush\_time severity: warn This option might decrease performance greatly. - have\_bdb severity: note The BDB engine is deprecated. If you aren't using it, you should disable it with the skip\_bdb option. - init\_connect severity: note The init\_connect option is enabled on this server. - init\_file severity: note The init\_file option is enabled on this server. - init\_slave severity: note The init\_slave option is enabled on this server. - init\_replica severity: note The init\_replica option is enabled on this server. - innodb\_additional\_mem\_pool\_size severity: warn This variable generally doesn't need to be larger than 20MB. - innodb\_buffer\_pool\_size severity: warn The InnoDB buffer pool size is unconfigured. In a production environment it should always be configured explicitly, and the default 10MB size is not good. - innodb\_checksums severity: warn InnoDB checksums are disabled. Your data is not protected from hardware corruption or other errors! - innodb\_doublewrite severity: warn InnoDB doublewrite is disabled. Unless you use a filesystem that protects against partial page writes, your data is not safe! - innodb\_fast\_shutdown severity: warn InnoDB's shutdown behavior is not the default. This can lead to poor performance, or the need to perform crash recovery upon startup. - innodb\_flush\_log\_at\_trx\_commit-1 severity: warn InnoDB is not configured in strictly ACID mode. If there is a crash, some transactions can be lost. - innodb\_flush\_log\_at\_trx\_commit-2 severity: warn Setting innodb\_flush\_log\_at\_trx\_commit to 0 has no performance benefits over setting it to 2, and more types of data loss are possible. If you are trying to change it from 1 for performance reasons, you should set it to 2 instead of 0. - innodb\_force\_recovery severity: warn InnoDB is in forced recovery mode! This should be used only temporarily when recovering from data corruption or other bugs, not for normal usage. - innodb\_lock\_wait\_timeout severity: warn This option has an unusually long value, which can cause system overload if locks are not being released. - innodb\_log\_buffer\_size severity: warn The InnoDB log buffer size generally should not be set larger than 16MB. If you are doing large BLOB operations, InnoDB is not really a good choice of engines anyway. - innodb\_log\_file\_size severity: warn The InnoDB log file size is set to its default value, which is not usable on production systems. - innodb\_max\_dirty\_pages\_pct severity: note The innodb\_max\_dirty\_pages\_pct is lower than the default. This can cause overly aggressive flushing and add load to the I/O system. - flush\_time severity: warn This setting is likely to cause very bad performance every flush\_time seconds. - key\_buffer\_size severity: warn The key buffer size is set to its default value, which is not good for most production systems. In a production environment, key\_buffer\_size should be larger than the default 8MB size. - large\_pages severity: note Large pages are enabled. - locked\_in\_memory severity: note The server is locked in memory with --memlock. - log\_warnings-1 severity: note Log\_warnings is disabled, so unusual events such as statements unsafe for replication and aborted connections will not be logged to the error log. - log\_warnings-2 severity: note Log\_warnings must be set greater than 1 to log unusual events such as aborted connections. - low\_priority\_updates severity: note The server is running with non-default lock priority for updates. This could cause update queries to wait unexpectedly for read queries. - max\_binlog\_size severity: note The max\_binlog\_size is smaller than the default of 1GB. - max\_connect\_errors severity: note max\_connect\_errors should probably be set as large as your platform allows. - max\_connections severity: warn If the server ever really has more than a thousand threads running, then the system is likely to spend more time scheduling threads than really doing useful work. This variable's value should be considered in light of your workload. - myisam\_repair\_threads severity: note myisam\_repair\_threads \> 1 enables multi-threaded repair, which is relatively untested and is still listed as beta-quality code in the official documentation. - old\_passwords severity: warn Old-style passwords are insecure. They are sent in plain text across the wire. - optimizer\_prune\_level severity: warn The optimizer will use an exhaustive search when planning complex queries, which can cause the planning process to take a long time. - port severity: note The server is listening on a non-default port. - query\_cache\_size-1 severity: note The query cache does not scale to large sizes and can cause unstable performance when larger than 128MB, especially on multi-core machines. - query\_cache\_size-2 severity: warn The query cache can cause severe performance problems when it is larger than 256MB, especially on multi-core machines. - query\_cache\_size-3 severity: note The query cache can cause severe performance problems when it is enabled, especially in high concurrent loads on multi-core machines. - read\_buffer\_size-1 severity: note The read\_buffer\_size variable should generally be left at its default unless an expert determines it is necessary to change it. - read\_buffer\_size-2 severity: warn The read\_buffer\_size variable should not be larger than 8MB. It should generally be left at its default unless an expert determines it is necessary to change it. Making it larger than 2MB can hurt performance significantly, and can make the server crash, swap to death, or just become extremely unstable. - read\_rnd\_buffer\_size-1 severity: note The read\_rnd\_buffer\_size variable should generally be left at its default unless an expert determines it is necessary to change it. - read\_rnd\_buffer\_size-2 severity: warn The read\_rnd\_buffer\_size variable should not be larger than 4M. It should generally be left at its default unless an expert determines it is necessary to change it. - relay\_log\_space\_limit severity: warn Setting relay\_log\_space\_limit can cause replicas to stop fetching binary logs from their source immediately. This could increase the risk that your data will be lost if the replication source crashes. If the replicas have encountered a limit on relay log space, then it is possible that the latest transactions exist only on the source and no replica has retrieved them. - slave\_net\_timeout severity: warn This variable is set too high. This is too long to wait before noticing that the connection to the replication source has failed and retrying. This should probably be set to 60 seconds or less. It is also a good idea to use pt-heartbeat to ensure that the connection does not appear to time out when the source is simply idle. - replica\_net\_timeout severity: warn This variable is set too high. This is too long to wait before noticing that the connection to the replication source has failed and retrying. This should probably be set to 60 seconds or less. It is also a good idea to use pt-heartbeat to ensure that the connection does not appear to time out when the source is simply idle. - slave\_skip\_errors severity: crit You should not set this option. If replication is having errors, you need to find and resolve the cause of that; it is likely that your replica's data is different from the source. You can find out with pt-table-checksum. - replica\_skip\_errors severity: crit You should not set this option. If replication is having errors, you need to find and resolve the cause of that; it is likely that your replica's data is different from the source. You can find out with pt-table-checksum. - sort\_buffer\_size-1 severity: note The sort\_buffer\_size variable should generally be left at its default unless an expert determines it is necessary to change it. - sort\_buffer\_size-2 severity: note The sort\_buffer\_size variable should generally be left at its default unless an expert determines it is necessary to change it. Making it larger than a few MB can hurt performance significantly, and can make the server crash, swap to death, or just become extremely unstable. - sql\_notes severity: note This server is configured not to log Note level warnings to the error log. - sync\_frm severity: warn It is best to set sync\_frm so that .frm files are flushed safely to disk in case of a server crash. - tx\_isolation-1 severity: note This server's transaction isolation level is non-default. - tx\_isolation-2 severity: warn Most applications should use the default REPEATABLE-READ transaction isolation level, or in a few cases READ-COMMITTED. - expire\_logs\_days severity: warn Binary logs are enabled, but automatic purging is not enabled. If you do not purge binary logs, your disk will fill up. If you delete binary logs externally to MySQL, you will cause unwanted behaviors. Always ask MySQL to purge obsolete logs, never delete them externally. - innodb\_file\_io\_threads severity: note This option is useless except on Windows. - innodb\_data\_file\_path severity: note Auto-extending InnoDB files can consume a lot of disk space that is very difficult to reclaim later. Some people prefer to set innodb\_file\_per\_table and allocate a fixed-size file for ibdata1. - innodb\_flush\_method severity: note Most production database servers that use InnoDB should set innodb\_flush\_method to O\_DIRECT to avoid double-buffering, unless the I/O system is very low performance. - innodb\_locks\_unsafe\_for\_binlog severity: warn This option makes point-in-time recovery from binary logs, and replication, untrustworthy if statement-based logging is used. - innodb\_support\_xa severity: warn MySQL's internal XA transaction support between InnoDB and the binary log is disabled. The binary log might not match InnoDB's state after crash recovery, and replication might drift out of sync due to out-of-order statements in the binary log. - log\_bin severity: warn Binary logging is disabled, so point-in-time recovery and replication are not possible. - log\_output severity: warn Directing log output to tables has a high performance impact. - max\_relay\_log\_size severity: note A custom max\_relay\_log\_size is defined. - myisam\_recover\_options severity: warn myisam\_recover\_options should be set to some value such as BACKUP,FORCE to ensure that table corruption is noticed. - storage\_engine severity: note The server is using a non-standard storage engine as default. - sync\_binlog severity: warn Binary logging is enabled, but sync\_binlog isn't configured so that every transaction is flushed to the binary log for durability. - tmp\_table\_size severity: note The effective minimum size of in-memory implicit temporary tables used internally during query execution is min(tmp\_table\_size, max\_heap\_table\_size), so max\_heap\_table\_size should be at least as large as tmp\_table\_size. - old mysql version severity: warn These are the recommended minimum version for each major release: 3.23, 4.1.20, 5.0.37, 5.1.30, 5.5.8, 5.6.10, 5.7.9, 8.0.11. This option does not complain about Innovation releases. - end-of-life mysql version severity: note Every release older than 8.0 is now officially end-of-life. ## OPTIONS This tool accepts additional command-line arguments. Refer to the "SYNOPSIS" and usage information for details. - \--ask-pass Prompt for a password when connecting to MySQL. - \--\[no\]buffer-stdout default: yes Enables STDOUT buffering. Disable this option if you want to see live progress when using output post-processing tools such as `"tee"` or `"kubectl logs"`. - \--charset short form: -A; type: string Default character set. If the value is utf8, sets Perl's binmode on STDOUT to utf8, passes the mysql\_enable\_utf8 option to DBD::mysql, and runs SET NAMES UTF8 after connecting to MySQL. Any other value sets binmode on STDOUT without the utf8 layer, and runs SET NAMES after connecting to MySQL. - \--config type: Array Read this comma-separated list of config files; if specified, this must be the first option on the command line. - \--daemonize Fork to the background and detach from the shell. POSIX operating systems only. - \--database short form: -D; type: string Connect to this database. - \--defaults-file short form: -F; type: string Only read mysql options from the given file. You must give an absolute pathname. - \--help Show help and exit. - \--host short form: -h; type: string Connect to host. - \--ignore-rules type: hash Ignore these rule IDs. Specify a comma-separated list of rule IDs (e.g. LIT.001,RES.002,etc.) to ignore. - \--mysql\_ssl short form: -s; type: int Create SSL MySQL connection. - \--password short form: -p; type: string Password to use when connecting. If password contains commas they must be escaped with a backslash: "exam\\,ple" - \--pid type: string Create the given PID file. The tool won't start if the PID file already exists and the PID it contains is different than the current PID. However, if the PID file exists and the PID it contains is no longer running, the tool will overwrite the PID file with the current PID. The PID file is removed automatically when the tool exits. - \--port short form: -P; type: int Port number to use for connection. - \--set-vars type: Array Set the MySQL variables in this comma-separated list of `"variable=value"` pairs. By default, the tool sets: ``` wait_timeout=10000 ``` Variables specified on the command line override these defaults. For example, specifying `"--set-vars wait_timeout=500"` overrides the defaultvalue of `10000`. The tool prints a warning and continues if a variable cannot be set. - \--socket short form: -S; type: string Socket file to use for connection. - \--source-of-variables type: string; default: mysql Read `"SHOW VARIABLES"` from this source. Possible values are "mysql", "none" or a file name. If "mysql" is specified then you must also specify a DSN on the command line. - \--user short form: -u; type: string User for login if not current user. - \--verbose short form: -v; cumulative: yes; default: 1 Increase verbosity of output. At the default level of verbosity, the program prints only the first sentence of each rule's description. At higher levels, the program prints more of the description. - \--version Show version and exit. - \--\[no\]version-check default: yes Check for the latest version of Percona Toolkit, MySQL, and other programs. This is a standard "check for updates automatically" feature, with two additional features. First, the tool checks its own version and also the versions of the following software: operating system, Percona Monitoring and Management (PMM), MySQL, Perl, MySQL driver for Perl (DBD::mysql), and Percona Toolkit. Second, it checks for and warns about versions with known problems. For example, MySQL 5.5.25 had a critical bug and was re-released as 5.5.25a. A secure connection to Percona’s Version Check database server is done to perform these checks. Each request is logged by the server, including software version numbers and unique ID of the checked system. The ID is generated by the Percona Toolkit installation script or when the Version Check database call is done for the first time. Any updates or known problems are printed to STDOUT before the tool's normal output. This feature should never interfere with the normal operation of the tool. For more information, visit \. ## DSN OPTIONS These DSN options are used to create a DSN. Each option is given like `"option=value"`. The options are case-sensitive, so P and p are not the same option. There cannot be whitespace before or after the `"="` and if the value contains whitespace it must be quoted. DSN options are comma-separated. See the percona-toolkit manpage for full details. - • A dsn: charset; copy: yes Default character set. - • D dsn: database; copy: yes Default database. - • F dsn: mysql\_read\_default\_file; copy: yes Only read default options from the given file - • h dsn: host; copy: yes Connect to host. - • p dsn: password; copy: yes Password to use when connecting. If password contains commas they must be escaped with a backslash: "exam\\,ple" - • P dsn: port; copy: yes Port number to use for connection. - • S dsn: mysql\_socket; copy: yes Socket file to use for connection. - • u dsn: user; copy: yes User for login if not current user. - • s dsn: mysql\_ssl; copy: yes Create SSL connection ## ENVIRONMENT The environment variable `"PTDEBUG"` enables verbose debugging output to STDERR. To enable debugging and capture all output to a file, run the tool like: ``` PTDEBUG=1 pt-variable-advisor ... > FILE 2>&1 ``` Be careful: debugging output is voluminous and can generate several megabytes of output. ## ATTENTION Using \ might expose passwords. When debug is enabled, all command line parameters are shown in the output. ## SYSTEM REQUIREMENTS You need Perl, DBI, DBD::mysql, and some core packages that ought to be installed in any reasonably new version of Perl. ## BUGS For a list of known bugs, see \. Please report bugs at \. Include the following information in your bug report: - • Complete command-line used to run the tool - • Tool "--version" - • MySQL version of all servers involved - • Output from the tool including STDERR - • Input files (log/dump/config files, etc.) If possible, include debugging output by running the tool with `"PTDEBUG"`; see "ENVIRONMENT". ## DOWNLOADING Visit \ to download the latest release of Percona Toolkit. Or, get the latest release from the command line: ``` wget percona.com/get/percona-toolkit.tar.gz wget percona.com/get/percona-toolkit.rpm wget percona.com/get/percona-toolkit.deb ``` You can also get individual tools from the latest release: ``` wget percona.com/get/TOOL ``` Replace `"TOOL"` with the name of any tool. ## AUTHORS Baron Schwartz and Daniel Nichter ## ABOUT PERCONA TOOLKIT This tool is part of Percona Toolkit, a collection of advanced command-line tools for MySQL developed by Percona. Percona Toolkit was forked from two projects in June, 2011: Maatkit and Aspersa. Those projects were created by Baron Schwartz and primarily developed by him and Daniel Nichter. Visit \ to learn about other free, open-source software from Percona. ## COPYRIGHT, LICENSE, AND WARRANTY This program is copyright 2010-2026 Percona LLC and/or its affiliates. THIS PROGRAM IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2; OR the Perl Artistic License. On UNIX and similar systems, you can issue \`man perlgpl' or \`man perlartistic' to read these licenses. You should have received a copy of the GNU General Public License, version 2 along with this program; if not, see \. ## VERSION pt-variable-advisor 3.7.1-4 ## POD ERRORS Hey! **The above document had some coding errors, which are explained below:** - Around line 6261: Non-ASCII character seen before =encoding in 'Percona’s'. Assuming UTF-8