Skip to content

pt-duplicate-key-checker

NAME

pt-duplicate-key-checker - Find duplicate indexes and foreign keys on MySQL tables.

SYNOPSIS

Usage

pt-duplicate-key-checker [OPTIONS] [DSN]

pt-duplicate-key-checker examines MySQL tables for duplicate or redundant indexes and foreign keys. Connection options are read from MySQL option files.

pt-duplicate-key-checker --host host1

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

This program examines the output of SHOW CREATE TABLE on MySQL tables, and if it finds indexes that cover the same columns as another index in the same order, or cover an exact leftmost prefix of another index, it prints out the suspicious indexes. By default, indexes must be of the same type, so a BTREE index is not a duplicate of a FULLTEXT index, even if they have the same columns. You can override this.

It also looks for duplicate foreign keys. A duplicate foreign key covers the same columns as another in the same table, and references the same parent table.

The output ends with a short summary that includes an estimate of the total size, in bytes, that the duplicate indexes are using. This is calculated by multiplying the index length by the number of rows in their respective tables.

OPTIONS

This tool accepts additional command-line arguments. Refer to the “SYNOPSIS” and usage information for details.

--all-structs

Compare indexes with different structs (BTREE, HASH, etc).

By default this is disabled, because a BTREE index that covers the same columns as a FULLTEXT index is not really a duplicate, for example.

--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.

--[no]clustered

default: yes

PK columns appended to secondary key is duplicate.

Detects when a suffix of a secondary key is a leftmost prefix of the primary key, and treats it as a duplicate key. Only detects this condition on storage engines whose primary keys are clustered (currently InnoDB and solidDB).

Clustered storage engines append the primary key columns to the leaf nodes of all secondary keys anyway, so you might consider it redundant to have them appear in the internal nodes as well. Of course, you may also want them in the internal nodes, because just having them at the leaf nodes won’t help for some queries. It does help for covering index queries, however.

Here’s an example of a key that is considered redundant with this option:

PRIMARY KEY  (`a`)
KEY `b` (`b`,`a`)

The use of such indexes is rather subtle. For example, suppose you have the following query:

SELECT ... WHERE b=1 ORDER BY a;

This query will do a filesort if we remove the index on b,a. But if we shorten the index on b,a to just b and also remove the ORDER BY, the query should return the same results.

The tool suggests shortening duplicate clustered keys by dropping the key and re-adding it without the primary key prefix. The shortened clustered key may still duplicate another key, but the tool cannot currently detect when this happens without being ran a second time to re-check the newly shortened clustered keys. Therefore, if you shorten any duplicate clustered keys, you should run the tool again.

--config

type: Array

Read this comma-separated list of config files; if specified, this must be the first option on the command line.

--databases

short form: -d; type: hash

Check only this comma-separated list of databases.

--defaults-file

short form: -F; type: string

Only read mysql options from the given file. You must give an absolute pathname.

--engines

short form: -e; type: hash

Check only tables whose storage engine is in this comma-separated list.

--help

Show help and exit.

--host

short form: -h; type: string

Connect to host.

--ignore-databases

type: Hash

Ignore this comma-separated list of databases.

--ignore-engines

type: Hash

Ignore this comma-separated list of storage engines.

--ignore-order

Ignore index order so KEY(a,b) duplicates KEY(b,a).

--ignore-tables

type: Hash

Ignore this comma-separated list of tables. Table names may be qualified with the database name.

--key-types

type: string; default: fk

Check for duplicate f=foreign keys, k=keys or fk=both.

--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.

--[no]sql

default: yes

Print DROP KEY statement for each duplicate key. By default an ALTER TABLE DROP KEY statement is printed below each duplicate key so that, if you want to remove the duplicate key, you can copy-paste the statement into MySQL.

To disable printing these statements, specify --no-sql.

--[no]summary

default: yes

Print summary of indexes at end of output.

--tables

short form: -t; type: hash

Check only this comma-separated list of tables.

Table names may be qualified with the database name.

--user

short form: -u; type: string

User for login if not current user.

--verbose

short form: -v

Output all keys and/or foreign keys found, not just redundant ones.

--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 its own version and also the versions of the following software: operating system, Percona Monitoring and Management (PMM), MySQL, Perl, MySQL driver for Perl (DBD::mysql), and Percona Toolkit. 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.

A secure connection to Percona’s Version Check database server is done to perform these checks. Each request is logged by the server, including software version numbers and unique ID of the checked system. The ID is generated by the Percona Toolkit installation script or when the Version Check database call is done for the first time.

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/doc/percona-toolkit/LATEST/version-check.html.

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-duplicate-key-checker ... > FILE 2>&1

Be careful: debugging output is voluminous and can generate several megabytes of output.

ATTENTION

Using <PTDEBUG> might expose passwords. When debug is enabled, all command line parameters are shown in the 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 https://jira.percona.com/projects/PT/issues.

Please report bugs at https://jira.percona.com/projects/PT. 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 for MySQL developed by Percona. Percona Toolkit was forked from two projects in June, 2011: Maatkit and Aspersa. Those projects were created by Baron Schwartz and primarily developed by him and Daniel Nichter. Visit http://www.percona.com/software/ to learn about other free, open-source software from Percona.

VERSION

pt-duplicate-key-checker 3.6.0