Provided by: percona-toolkit_3.0.13-1_all bug


       pt-variable-advisor - Analyze MySQL variables and advise on possible problems.


       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


       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,

       ·   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


       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.

       At the time of this release, pt-variable-advisor only examples "SHOW VARIABLES", but other
       input sources are planned like "SHOW STATUS" and "SHOW SLAVE STATUS".


       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.

           severity: note

           Are you trying to write to more than one server in a dual-master 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.

           severity: note

           Holes (spaces left by deletes) in MyISAM tables might never be reused.

           severity: note

           A large value of this setting can create a denial of service vulnerability.

           severity: crit

           Servers built with debugging capability should not be used in production because of
           the large performance impact.

           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.

           severity: warn

           This option might decrease performance greatly.

           severity: warn

           This option might decrease performance greatly.

           severity: note

           The BDB engine is deprecated.  If you aren't using it, you should disable it with the
           skip_bdb option.

           severity: note

           The init_connect option is enabled on this server.

           severity: note

           The init_file option is enabled on this server.

           severity: note

           The init_slave option is enabled on this server.

           severity: warn

           This variable generally doesn't need to be larger than 20MB.

           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.

           severity: warn

           InnoDB checksums are disabled.  Your data is not protected from hardware corruption or
           other errors!

           severity: warn

           InnoDB doublewrite is disabled.  Unless you use a filesystem that protects against
           partial page writes, your data is not safe!

           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.

           severity: warn

           InnoDB is not configured in strictly ACID mode.  If there is a crash, some
           transactions can be lost.

           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.

           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.

           severity: warn

           This option has an unusually long value, which can cause system overload if locks are
           not being released.

           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.

           severity: warn

           The InnoDB log file size is set to its default value, which is not usable on
           production systems.

           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.

           severity: warn

           This setting is likely to cause very bad performance every flush_time seconds.

           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.

           severity: note

           Large pages are enabled.

           severity: note

           The server is locked in memory with --memlock.

           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.

           severity: note

           Log_warnings must be set greater than 1 to log unusual events such as aborted

           severity: note

           The server is running with non-default lock priority for updates.  This could cause
           update queries to wait unexpectedly for read queries.

           severity: note

           The max_binlog_size is smaller than the default of 1GB.

           severity: note

           max_connect_errors should probably be set as large as your platform allows.

           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.

           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.

           severity: warn

           Old-style passwords are insecure.  They are sent in plain text across the wire.

           severity: warn

           The optimizer will use an exhaustive search when planning complex queries, which can
           cause the planning process to take a long time.

           severity: note

           The server is listening on a non-default port.

           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.

           severity: warn

           The query cache can cause severe performance problems when it is larger than 256MB,
           especially on multi-core machines.

           severity: note

           The read_buffer_size variable should generally be left at its default unless an expert
           determines it is necessary to change it.

           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.

           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.

           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.

           severity: warn

           Setting relay_log_space_limit can cause replicas to stop fetching binary logs from
           their master immediately. This could increase the risk that your data will be lost if
           the master crashes. If the replicas have encountered a limit on relay log space, then
           it is possible that the latest transactions exist only on the master and no replica
           has retrieved them.

           severity: warn

           This variable is set too high.  This is too long to wait before noticing that the
           connection to the master 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 master is simply idle.

           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 slave's data is different from the
           master.  You can find out with pt-table-checksum.

           severity: note

           The sort_buffer_size variable should generally be left at its default unless an expert
           determines it is necessary to change it.

           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.

           severity: note

           This server is configured not to log Note level warnings to the error log.

           severity: warn

           It is best to set sync_frm so that .frm files are flushed safely to disk in case of a
           server crash.

           severity: note

           This server's transaction isolation level is non-default.

           severity: warn

           Most applications should use the default REPEATABLE-READ transaction isolation level,
           or in a few cases READ-COMMITTED.

           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.

           severity: note

           This option is useless except on Windows.

           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.

           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.

           severity: warn

           This option makes point-in-time recovery from binary logs, and replication,
           untrustworthy if statement-based logging is used.

           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.

           severity: warn

           Binary logging is disabled, so point-in-time recovery and replication are not

           severity: warn

           Directing log output to tables has a high performance impact.

           severity: note

           A custom max_relay_log_size is defined.

           severity: warn

           myisam_recover_options should be set to some value such as BACKUP,FORCE to ensure that
           table corruption is noticed.

           severity: note

           The server is using a non-standard storage engine as default.

           severity: warn

           Binary logging is enabled, but sync_binlog isn't configured so that every transaction
           is flushed to the binary log for durability.

           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.

       end-of-life mysql version
           severity: note

           Every release older than 5.1 is now officially end-of-life.


       This tool accepts additional command-line arguments.  Refer to the "SYNOPSIS" and usage
       information for details.

           Prompt for a password when connecting to MySQL.

           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.

           type: Array

           Read this comma-separated list of config files; if specified, this must be the first
           option on the command line.

           Fork to the background and detach from the shell.  POSIX operating systems only.

           short form: -D; type: string

           Connect to this database.

           short form: -F; type: string

           Only read mysql options from the given file.  You must give an absolute pathname.

           Show help and exit.

           short form: -h; type: string

           Connect to host.

           type: hash

           Ignore these rule IDs.

           Specify a comma-separated list of rule IDs (e.g. LIT.001,RES.002,etc.)  to ignore.

           short form: -p; type: string

           Password to use when connecting.  If password contains commas they must be escaped
           with a backslash: "exam\,ple"

           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.

           short form: -P; type: int

           Port number to use for connection.

           type: Array

           Set the MySQL variables in this comma-separated list of "variable=value" pairs.

           By default, the tool sets:


           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.

           short form: -S; type: string

           Socket file to use for connection.

           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.

           short form: -u; type: string

           User for login if not current user.

           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.

           Show version and exit.

           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

           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


       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.


       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.


       You need Perl, DBI, DBD::mysql, and some core packages that ought to be installed in any
       reasonably new version of Perl.


       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


       Visit <> to download the latest release of
       Percona Toolkit.  Or, get the latest release from the command line:




       You can also get individual tools from the latest release:


       Replace "TOOL" with the name of any tool.


       Baron Schwartz and Daniel Nichter


       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.


       This program is copyright 2010-2018 Percona LLC and/or its affiliates.


       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 along with this program;
       if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
       MA  02111-1307  USA.


       pt-variable-advisor 3.0.13


       Hey! The above document had some coding errors, which are explained below:

       Around line 6073:
           Non-ASCII character seen before =encoding in 'Percona’s'. Assuming UTF-8