.. program:: pt-variable-advisor ================================ :program:`pt-variable-advisor` ================================ .. highlight:: perl NAME ==== :program:`pt-variable-advisor` - Analyze |MySQL| variables and advise on possible problems. SYNOPSIS ======== Usage ----- :: pt-variable-advisor [OPTION...] [DSN] :program:`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. :program:`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 `_. See also :ref:`bugs` for more information on filing bugs and getting help. DESCRIPTION =========== :program:`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, :program:`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 :program:`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. .. option:: --ask-pass Prompt for a password when connecting to |MySQL|. .. option:: --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|. .. option:: --config type: Array Read this comma-separated list of config files; if specified, this must be the first option on the command line. .. option:: --daemonize Fork to the background and detach from the shell. POSIX operating systems only. .. option:: --defaults-file short form: -F; type: string Only read mysql options from the given file. You must give an absolute pathname. .. option:: --help Show help and exit. .. option:: --host short form: -h; type: string Connect to host. .. option:: --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. .. option:: --password short form: -p; type: string Password to use when connecting. .. option:: --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. .. option:: --port short form: -P; type: int Port number to use for connection. .. option:: --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. .. option:: --socket short form: -S; type: string Socket file to use for connection. .. option:: --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. .. option:: --user short form: -u; type: string User for login if not current user. .. option:: --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. .. option:: --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 :program:`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 `_. Please report bugs at `https://bugs.launchpad.net/percona-toolkit `_. AUTHORS ======= *Baron Schwartz* and *Daniel Nichter* COPYRIGHT, LICENSE, AND WARRANTY ================================ This program is copyright 2010-2011 Percona Inc. Feedback and improvements are welcome. VERSION ======= :program:`pt-variable-advisor` 1.0.1