pt-query-advisor

pt-query-advisor

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.

CLA.002

severity: note

ORDER BY RAND(). ORDER BY RAND() is a very inefficient way to retrieve a random row from the results.

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.

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.

CLA.006

severity: warn

GROUP BY or ORDER BY different tables will force a temp table and filesort.

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; 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 differs between some MySQL versions.

JOI.002

severity: crit

A table is joined twice. The same table appears at least twice in the FROM clause.

JOI.003

severity: warn

Reference to outer table column in WHERE clause prevents OUTER JOIN, implicitly converts to INNER JOIN.

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

!= is non-standard. Use the <> operator to test for inequality.

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 individually
--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.

--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 http://www.percona.com/software/ for more software developed by Percona.

VERSION

pt-query-advisor 2.0.5

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