Provided by: percona-toolkit_3.2.1-1_all 
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.
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-duplicate-key-checker>.
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.
COPYRIGHT, LICENSE, AND WARRANTY
This program is copyright 2011-2018 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 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-duplicate-key-checker 3.2.1
POD ERRORS
Hey! The above document had some coding errors, which are explained below:
Around line 5602:
Non-ASCII character seen before =encoding in 'Percona’s'. Assuming UTF-8
perl v5.30.3 2020-08-30 PT-DUPLICATE-KEY-CHECKER(1p)