--- name: "pt-query-advisor" section: "1p" platform: "linux" package: "percona-toolkit" version: "2.1.2-1" release: "Debian 7 (Wheezy)" platforms: ["linux"] url: "https://new.carta.tech/pt-query-advisor" --- # pt-query-advisor(1p) Analyze queries and advise on possible problems. ## NAME pt-query-advisor - Analyze queries and advise on possible problems. ## SYNOPSIS Usage: pt-query-advisor \[OPTION...\] \[FILE\] pt-query-advisor analyzes queries and advises on possible problems. It can read queries from several types of log files, or you can use the --query or --review options. To analyze all queries in a MySQL slow query log file: ``` pt-query-advisor /path/to/slow-query.log ``` ## 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-query-advisor simply reads queries and examines them, and is thus very low risk. At the time of this release we know of no issues that could harm 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-query-advisor \. See also "BUGS" for more information on filing bugs and getting help. ## DESCRIPTION pt-query-advisor applies rules to queries, looking for potential problems. It prints a report of queries that match rules. ## RULES These are the rules that pt-query-advisor will apply to the queries it examines. Each rule has three bits of information: an ID, a severity and a description. The rule's ID is its identifier. We use a seven-character ID, and the naming convention is three characters, a period, and a three-digit number. The first three characters are sort of an abbreviation of the general class of the rule. For example, ALI.001 is some rule related to how the query uses aliases. 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 query 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. - ALI.001 severity: note Aliasing without the AS keyword. Explicitly using the AS keyword in column or table aliases, such as "tbl AS alias," is more readable than implicit aliases such as "tbl alias". - ALI.002 severity: warn Aliasing the '\*' wildcard. Aliasing a column wildcard, such as "SELECT tbl.\* col1, col2" probably indicates a bug in your SQL. You probably meant for the query to retrieve col1, but instead it renames the last column in the \*-wildcarded list. - ALI.003 severity: note Aliasing without renaming. The table or column's alias is the same as its real name, and the alias just makes the query harder to read. - ARG.001 severity: warn Argument with leading wildcard. An argument has a leading wildcard character, such as "%foo". The predicate with this argument is not sargable and cannot use an index if one exists. - ARG.002 severity: note LIKE without a wildcard. A LIKE pattern that does not include a wildcard is potentially a bug in the SQL. - CLA.001 severity: warn SELECT without WHERE. The SELECT statement has no WHERE clause and could examine many more rows than intended. - CLA.002 severity: note ORDER BY *RAND()*. ORDER BY *RAND()* is a very inefficient way to retrieve a random row from the results, because it sorts the entire result and then throws most of it away. - CLA.003 severity: note LIMIT with OFFSET. Paginating a result set with LIMIT and OFFSET is O(n^2) complexity, and will cause performance problems as the data grows larger. Pagination techniques such as bookmarked scans are much more efficient. - CLA.004 severity: note Ordinal in the GROUP BY clause. Using a number in the GROUP BY clause, instead of an expression or column name, can cause problems if the query is changed. - CLA.005 severity: warn ORDER BY constant column. This is probably a bug in your SQL; at best it is a useless operation that does not change the query results. - CLA.006 severity: warn GROUP BY or ORDER BY on different tables. This will force the use of a temporary table and filesort, which can be a huge performance problem and can consume large amounts of memory and temporary space on disk. - CLA.007 severity: warn ORDER BY clauses that sort the results in different directions prevents indexes from being used. All expressions in the ORDER BY clause must be ordered either ASC or DESC so that MySQL can use an index. - COL.001 severity: note SELECT \*. Selecting all columns with the \* wildcard will cause the query's meaning and behavior to change if the table's schema changes, and might cause the query to retrieve too much data. - COL.002 severity: note Blind INSERT. The INSERT or REPLACE query doesn't specify the columns explicitly, so the query's behavior will change if the table's schema changes; use "INSERT INTO tbl(col1, col2) VALUES..." instead. - LIT.001 severity: warn Storing an IP address as characters. The string literal looks like an IP address, but is not an argument to *INET\_ATON()*, indicating that the data is stored as characters instead of as integers. It is more efficient to store IP addresses as integers. - LIT.002 severity: warn Unquoted date/time literal. A query such as "WHERE col\<2010-02-12" is valid SQL but is probably a bug, because it will be interpreted as "WHERE col\<1996"; the literal should be quoted. - KWR.001 severity: note SQL\_CALC\_FOUND\_ROWS is inefficient. SQL\_CALC\_FOUND\_ROWS can cause performance problems because it does not scale well; use alternative strategies to build functionality such as paginated result screens. - JOI.001 severity: crit Mixing comma and ANSI joins. Mixing comma joins and ANSI joins is confusing to humans, and the behavior and precedence differs between some MySQL versions, which can introduce bugs. - JOI.002 severity: crit A table is joined twice. The same table appears at least twice in the FROM clause in a manner that can be reduced to a single access to the table. - JOI.003 severity: warn OUTER JOIN defeated. The reference to an outer table column in the WHERE clause prevents the OUTER JOIN from returning any non-matched rows, which implicitly converts the query to an INNER JOIN. This is probably a bug in the query or a misunderstanding of how OUTER JOIN works. - JOI.004 severity: warn Exclusion join uses wrong column in WHERE. The exclusion join (LEFT OUTER JOIN with a WHERE clause that is satisfied only if there is no row in the right-hand table) seems to use the wrong column in the WHERE clause. A query such as "... FROM l LEFT OUTER JOIN r ON l.l=r.r WHERE r.z IS NULL" probably ought to list r.r in the WHERE IS NULL clause. - RES.001 severity: warn Non-deterministic GROUP BY. The SQL retrieves columns that are neither in an aggregate function nor the GROUP BY expression, so these values will be non-deterministic in the result. - RES.002 severity: warn LIMIT without ORDER BY. LIMIT without ORDER BY causes non-deterministic results, depending on the query execution plan. - STA.001 severity: note The != operator is non-standard. Use the \<\> operator to test for inequality instead. - SUB.001 severity: crit *IN()* and NOT *IN()* subqueries are poorly optimized. MySQL executes the subquery as a dependent subquery for each row in the outer query. This is a frequent cause of serious performance problems. This might improve in version 5.6 of MySQL, but for versions 5.1 and older, the query should be rewritten as a JOIN or a LEFT OUTER JOIN, respectively. ## OPTIONS "--query" and "--review" are mutually exclusive. 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. - \--\[no\]continue-on-error default: yes Continue working even if there is an error. - \--daemonize Fork to the background and detach from the shell. POSIX operating systems only. - \--database short form: -D; type: string Connect to this database. This is also used as the default database for "--\[no\]show-create-table" if a query does not use database-qualified tables. - \--defaults-file short form: -F; type: string Only read mysql options from the given file. You must give an absolute pathname. - \--group-by type: string; default: rule\_id Group items in the report by this attribute. Possible attributes are: ``` ATTRIBUTE GROUPS ========= ======================================================== rule_id Items matching the same rule ID query_id Queries with the same ID (the same fingerprint) none No grouping, report each query and its advice separately ``` - \--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. Currently, the rule IDs are case-sensitive and must be uppercase. - \--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. - \--print-all Print all queries, even those that do not match any rules. With "--group-by" `"none"`, non-matching queries are printed in the main report and profile. For other "--group-by" values, non-matching queries are only printed in the profile. Non-matching queries have zeros for `"NOTE"`, `"WARN"` and `"CRIT"` in the profile. - \--query type: string Analyze this single query and ignore files and STDIN. This option allows you to supply a single query on the command line. Any files also specified on the command line are ignored. - \--report-format type: string; default: compact Type of report format: full or compact. In full mode, every query's report contains the description of the rules it matched, even if this information was previously displayed. In compact mode, the repeated information is suppressed, and only the rule ID is displayed. - \--report-type type: Hash Alternative formats to output the report. Currently, only "json" is recognized -- anything else is ignored and the default behavior used. - \--review type: DSN Analyze queries from this pt-query-digest query review table. - \--sample type: int; default: 1 How many samples of the query to show. - \--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. - \--\[no\]show-create-table default: yes Get `"SHOW CREATE TABLE"` for each query's table. If host connection options are given (like "--host", "--port", etc.) then the tool will also get `"SHOW CREATE TABLE"` for each query. This information is needed for some rules like JOI.004. If this option is disabled by specifying `"--no-show-create-table"` then some rules may not be checked. - \--socket short form: -S; type: string Socket file to use for connection. - \--type type: Array The type of input to parse (default slowlog). The permitted types are slowlog and genlog. - \--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. See also "--report-format". - \--version Show version and exit. - \--where type: string Apply this WHERE clause to the SELECT query on the "--review" table. ## 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 Database that contains the query review table. - • 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. - • t Table to use as the query review table. - • 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-query-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-query-advisor \. Please report bugs at 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/ \ 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 \ 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-query-advisor 2.1.2