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percona-toolkit/docs/user/pt-variable-advisor.rst
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###################
pt-variable-advisor
###################
.. highlight:: perl
****
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:
.. code-block:: perl
pt-variable-advisor localhost
Get SHOW VARIABLES output saved in vars.txt:
.. code-block:: perl
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 is relatively rare, and could cause
an increased risk of previously unknown bugs in replication.
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.
\* 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.
\* 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.
***********
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:
.. code-block:: perl
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:
\* 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 `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:
.. code-block:: perl
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:
.. code-block:: perl
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/ <http://www.percona.com/software/>`_ for more software developed by Percona.
********************************
COPYRIGHT, LICENSE, AND WARRANTY
********************************
This program is copyright 2010-2011 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
*******
Percona Toolkit v0.9.5 released 2011-08-04
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