pt-variable-advisorp - Online in the Cloud

PROGRAM:

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.

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 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.

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_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.

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.

--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.

--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 the version of other programs on the local system in
addition to its own version. For example, it checks the version of every MySQL server
it connects to, Perl, and the Perl module DBD::mysql. 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.

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 <https://www.percona.com/version-check>.

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.

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.

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