PT-VARIABLE-ADVISOR(1p) User Contributed Perl Documentation PT-VARIABLE-ADVISOR(1p)
NAME
pt-variable-advisor - Analyze MySQL variables and advise on possible problems.
SYNOPSIS
Usage: pt-variable-advisor [OPTION...] [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
The following section is included to inform users about the potential risks, whether known or unknown, of using this tool. The two main
categories of risks are those created by the nature of the tool (e.g. read-only tools vs. read-write tools) and those created by bugs.
pt-variable-advisor reads MySQL's configuration and examines it and is thus very low risk.
At the time of this release, we know of no bugs that could cause serious harm to users.
The authoritative source for updated information is always the online issue tracking system. Issues that affect this tool will be marked
as such. You can see a list of such issues at the following URL: http://www.percona.com/bugs/pt-variable-advisor
<http://www.percona.com/bugs/pt-variable-advisor>.
See also "BUGS" for more information on filing bugs and getting help.
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.
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".
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-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.
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.
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 unconfigured. In a production environment it should always be configured explicitly, and the default 8MB size
is not good.
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.
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 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.
slave_net_timeout
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.
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 slave's data is different from the master. 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_log_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.
end-of-life mysql version
severity: note
Every release older than 5.1 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.
--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.
--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.
--password
short form: -p; type: string
Password to use when connecting.
--pid
type: string
Create the given PID file when daemonized. The file contains the process ID of the daemonized instance. The PID file is removed when
the daemonized instance exits. The program checks for the existence of the PID file when starting; if it exists and the process with
the matching PID exists, the program exits.
--port
short form: -P; type: int
Port number to use for connection.
--set-vars
type: string; default: wait_timeout=10000
Set these MySQL variables. Immediately after connecting to MySQL, this string will be appended to SET and executed.
--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.
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.
o A
dsn: charset; copy: yes
Default character set.
o D
dsn: database; copy: yes
Default database.
o F
dsn: mysql_read_default_file; copy: yes
Only read default options from the given file
o h
dsn: host; copy: yes
Connect to host.
o p
dsn: password; copy: yes
Password to use when connecting.
o P
dsn: port; copy: yes
Port number to use for connection.
o S
dsn: mysql_socket; copy: yes
Socket file to use for connection.
o u
dsn: user; copy: yes
User for login if not current user.
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.
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 http://www.percona.com/bugs/pt-variable-advisor <http://www.percona.com/bugs/pt-variable-advisor>.
Please report bugs at https://bugs.launchpad.net/percona-toolkit <https://bugs.launchpad.net/percona-toolkit>. Include the following
information in your bug report:
o Complete command-line used to run the tool
o Tool "--version"
o MySQL version of all servers involved
o Output from the tool including STDERR
o Input files (log/dump/config files, etc.)
If possible, include debugging output by running the tool with "PTDEBUG"; see "ENVIRONMENT".
DOWNLOADING
Visit http://www.percona.com/software/percona-toolkit/ <http://www.percona.com/software/percona-toolkit/> 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 developed by Percona for MySQL support and consulting.
Percona Toolkit was forked from two projects in June, 2011: Maatkit and Aspersa. Those projects were created by Baron Schwartz and
developed primarily by him and Daniel Nichter, both of whom are employed by Percona. Visit <http://www.percona.com/software/> for more
software developed by Percona.
COPYRIGHT, LICENSE, AND WARRANTY
This program is copyright 2010-2012 Percona Inc. Feedback and improvements are welcome.
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 along with this program; if not, write to the Free Software Foundation,
Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
VERSION
pt-variable-advisor 2.1.2
perl v5.14.2 2012-06-15 PT-VARIABLE-ADVISOR(1p)