PT-DUPL...CHECKER(1)

📦
version 3.7.1_4 · 5 versions
, in arch rolling

okay bestie, welcome to pt-duplicate-key-checker(1) — it’s a User Contributed Perl Documentation page, and it’s here to help you find duplicate indexes and foreign keys on MySQL tables. 💅✨

💖 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 💾
bestie, this is the serious part — databases are not the vibe to gamble with. 🔥

💅 DESCRIPTION 💅

So here’s the vibe: this program peeks at the output of SHOW CREATE TABLE on MySQL tables. If it spots indexes that cover the same columns as another index in the same order, or that cover an exact leftmost prefix of another index, it prints out the suspicious indexes. By default, indexes have to be 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 sniffs out duplicate foreign keys. A duplicate foreign key covers the same columns as another one in the same table, and references the same parent table. 🔑

The output wraps up with a short summary that includes an estimate of the total size, in bytes, that the duplicate indexes are using. That estimate 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. 🙈
  • --[no]buffer-stdout — default: yes. Enables STDOUT buffering. Disable this option if you want to see live progress when using output post-processing tools such as tee or kubectl logs. 💅
  • --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, TokuDB and MyRocks). 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. 📋
  • --invisible — the output SQL will make the index INVISIBLE, instead of dropping it. 👻 An invisible index cannot be considered by the query optimizer, but is still maintained when writes happen to the table. To make the index usable by the optimizer, execute ALTER INDEX .. VISIBLE. While dropping an index is a fast, background operation, adding indexes is a slow, CPU, and disk IO intensive operation. If you discover that an index was made invisible incorrectly, it becomes a NOOP (no-operation) to make the index visible again, compared to completely re-adding the index. 🫶
  • --key-types — type: string; default: fk. Check for duplicate f=foreign keys, k=keys or fk=both. 🔑
  • --mysql_ssl — short form: -s; type: int. Create SSL MySQL connection. 🔒
  • --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 default value 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. 👤
  • s — dsn: mysql_ssl; copy: yes. Create SSL connection. 🔐

🌈 ENVIRONMENT 🌈

okay so first up, the environment variable PTDEBUG turns on verbose debugging output to STDERR. slay for troubleshooting, but bestie, it does not hold back.

To enable debugging and capture all the output into a file, run the tool like this:

PTDEBUG=1 pt-duplicate-key-checker ... > FILE 2>&1
Be careful: debugging output is voluminous and can generate several megabytes of output. like, several megabytes megabytes. do not underestimate the lore.

🚨 ATTENTION 🚨

Using PTDEBUG might expose passwords. not me leaking the whole group chat 😭 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. that's the whole requirements list, bestie — no secret bonus quest ✨

🐛 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. the debug info really does help the maintainers help you 🫶

🛍️ 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. mix and match, bestie 🎀

👑 AUTHORS 👑

Baron Schwartz and Daniel Nichter

yes, those two. iconic behavior. 💅

🌸 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. the lore is literally right there ✨

This program is copyright 2011-2026 Percona LLC and/or its affiliates, 2007-2011 Baron Schwartz.

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, version 2 along with this program; if not, see https://www.gnu.org/licenses/. legal bestie has entered the chat, and she is thorough 🫶

🏷️ VERSION 🏷️

pt-duplicate-key-checker 3.7.1-4

that's the version, no cap ⭐

💀 POD ERRORS 💀

Hey! The above document had some coding errors, which are explained below:

Around line 5698: Non-ASCII character seen before =encoding in 'Percona’s'. Assuming UTF-8.

it's giving tiny documentation oopsie, not a whole crisis 🙈

💖 And that’s the whole vibe — the footer taps out at PT-DUPL...CHECKER(1), source/version perl v5.42.2, dated 2026-09-01. Go fix those duplicate keys, bestie, periodt. 🎀

📦 where this page comes from