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.\" ========================================================================
.\"
.IX Title "PT-DUPLICATE-KEY-CHECKER 1"
.TH PT-DUPLICATE-KEY-CHECKER 1 2025-01-01 "perl v5.40.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.SH NAME
pt\-duplicate\-key\-checker \- Find duplicate indexes and foreign keys on MySQL tables.
.SH SYNOPSIS
.IX Header "SYNOPSIS"
Usage: pt-duplicate-key-checker [OPTIONS] [DSN]
.PP
pt-duplicate-key-checker examines MySQL tables for duplicate or redundant
indexes and foreign keys.  Connection options are read from MySQL option files.
.PP
.Vb 1
\&   pt\-duplicate\-key\-checker \-\-host host1
.Ve
.SH RISKS
.IX Header "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:
.IP \(bu 4
Read the tool's documentation
.IP \(bu 4
Review the tool's known "BUGS"
.IP \(bu 4
Test the tool on a non-production server
.IP \(bu 4
Backup your production server and verify the backups
.SH DESCRIPTION
.IX Header "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.
.PP
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.
.PP
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.
.SH OPTIONS
.IX Header "OPTIONS"
This tool accepts additional command-line arguments.  Refer to the
"SYNOPSIS" and usage information for details.
.IP \-\-all\-structs 4
.IX Item "--all-structs"
Compare indexes with different structs (BTREE, HASH, etc).
.Sp
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.
.IP \-\-ask\-pass 4
.IX Item "--ask-pass"
Prompt for a password when connecting to MySQL.
.IP \-\-charset 4
.IX Item "--charset"
short form: \-A; type: string
.Sp
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.
.IP \-\-[no]clustered 4
.IX Item "--[no]clustered"
default: yes
.Sp
PK columns appended to secondary key is duplicate.
.Sp
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).
.Sp
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.
.Sp
Here's an example of a key that is considered redundant with this option:
.Sp
.Vb 2
\&  PRIMARY KEY  (\`a\`)
\&  KEY \`b\` (\`b\`,\`a\`)
.Ve
.Sp
The use of such indexes is rather subtle.  For example, suppose you have the
following query:
.Sp
.Vb 1
\&  SELECT ... WHERE b=1 ORDER BY a;
.Ve
.Sp
This query will do a filesort if we remove the index on \f(CW\*(C`b,a\*(C'\fR.  But if we
shorten the index on \f(CW\*(C`b,a\*(C'\fR to just \f(CW\*(C`b\*(C'\fR and also remove the ORDER BY, the query
should return the same results.
.Sp
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.
.IP \-\-config 4
.IX Item "--config"
type: Array
.Sp
Read this comma-separated list of config files; if specified, this must be the
first option on the command line.
.IP \-\-databases 4
.IX Item "--databases"
short form: \-d; type: hash
.Sp
Check only this comma-separated list of databases.
.IP \-\-defaults\-file 4
.IX Item "--defaults-file"
short form: \-F; type: string
.Sp
Only read mysql options from the given file.  You must give an absolute pathname.
.IP \-\-engines 4
.IX Item "--engines"
short form: \-e; type: hash
.Sp
Check only tables whose storage engine is in this comma-separated list.
.IP \-\-help 4
.IX Item "--help"
Show help and exit.
.IP \-\-host 4
.IX Item "--host"
short form: \-h; type: string
.Sp
Connect to host.
.IP \-\-ignore\-databases 4
.IX Item "--ignore-databases"
type: Hash
.Sp
Ignore this comma-separated list of databases.
.IP \-\-ignore\-engines 4
.IX Item "--ignore-engines"
type: Hash
.Sp
Ignore this comma-separated list of storage engines.
.IP \-\-ignore\-order 4
.IX Item "--ignore-order"
Ignore index order so KEY(a,b) duplicates KEY(b,a).
.IP \-\-ignore\-tables 4
.IX Item "--ignore-tables"
type: Hash
.Sp
Ignore this comma-separated list of tables.  Table names may be qualified with
the database name.
.IP \-\-key\-types 4
.IX Item "--key-types"
type: string; default: fk
.Sp
Check for duplicate f=foreign keys, k=keys or fk=both.
.IP \-\-password 4
.IX Item "--password"
short form: \-p; type: string
.Sp
Password to use when connecting.
If password contains commas they must be escaped with a backslash: "exam\e,ple"
.IP \-\-pid 4
.IX Item "--pid"
type: string
.Sp
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.
.IP \-\-port 4
.IX Item "--port"
short form: \-P; type: int
.Sp
Port number to use for connection.
.IP \-\-set\-vars 4
.IX Item "--set-vars"
type: Array
.Sp
Set the MySQL variables in this comma-separated list of \f(CW\*(C`variable=value\*(C'\fR pairs.
.Sp
By default, the tool sets:
.Sp
.Vb 1
\&   wait_timeout=10000
.Ve
.Sp
Variables specified on the command line override these defaults.  For
example, specifying \f(CW\*(C`\-\-set\-vars wait_timeout=500\*(C'\fR overrides the defaultvalue of \f(CW10000\fR.
.Sp
The tool prints a warning and continues if a variable cannot be set.
.IP \-\-socket 4
.IX Item "--socket"
short form: \-S; type: string
.Sp
Socket file to use for connection.
.IP \-\-[no]sql 4
.IX Item "--[no]sql"
default: yes
.Sp
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.
.Sp
To disable printing these statements, specify \f(CW\*(C`\-\-no\-sql\*(C'\fR.
.IP \-\-[no]summary 4
.IX Item "--[no]summary"
default: yes
.Sp
Print summary of indexes at end of output.
.IP \-\-tables 4
.IX Item "--tables"
short form: \-t; type: hash
.Sp
Check only this comma-separated list of tables.
.Sp
Table names may be qualified with the database name.
.IP \-\-user 4
.IX Item "--user"
short form: \-u; type: string
.Sp
User for login if not current user.
.IP \-\-verbose 4
.IX Item "--verbose"
short form: \-v
.Sp
Output all keys and/or foreign keys found, not just redundant ones.
.IP \-\-version 4
.IX Item "--version"
Show version and exit.
.IP \-\-[no]version\-check 4
.IX Item "--[no]version-check"
default: yes
.Sp
Check for the latest version of Percona Toolkit, MySQL, and other programs.
.Sp
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.
.Sp
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.
.Sp
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.
.Sp
For more information, visit <https://www.percona.com/doc/percona\-toolkit/LATEST/version\-check.html>.
.SH "DSN OPTIONS"
.IX Header "DSN OPTIONS"
These DSN options are used to create a DSN.  Each option is given like
\&\f(CW\*(C`option=value\*(C'\fR.  The options are case-sensitive, so P and p are not the
same option.  There cannot be whitespace before or after the \f(CW\*(C`=\*(C'\fR and
if the value contains whitespace it must be quoted.  DSN options are
comma-separated.  See the percona-toolkit manpage for full details.
.IP \(bu 4
A
.Sp
dsn: charset; copy: yes
.Sp
Default character set.
.IP \(bu 4
D
.Sp
dsn: database; copy: yes
.Sp
Default database.
.IP \(bu 4
F
.Sp
dsn: mysql_read_default_file; copy: yes
.Sp
Only read default options from the given file
.IP \(bu 4
h
.Sp
dsn: host; copy: yes
.Sp
Connect to host.
.IP \(bu 4
p
.Sp
dsn: password; copy: yes
.Sp
Password to use when connecting.
If password contains commas they must be escaped with a backslash: "exam\e,ple"
.IP \(bu 4
P
.Sp
dsn: port; copy: yes
.Sp
Port number to use for connection.
.IP \(bu 4
S
.Sp
dsn: mysql_socket; copy: yes
.Sp
Socket file to use for connection.
.IP \(bu 4
u
.Sp
dsn: user; copy: yes
.Sp
User for login if not current user.
.IP \(bu 4
s
.Sp
dsn: mysql_ssl; copy: yes
.Sp
Create SSL connection
.SH ENVIRONMENT
.IX Header "ENVIRONMENT"
The environment variable \f(CW\*(C`PTDEBUG\*(C'\fR enables verbose debugging output to STDERR.
To enable debugging and capture all output to a file, run the tool like:
.PP
.Vb 1
\&   PTDEBUG=1 pt\-duplicate\-key\-checker ... > FILE 2>&1
.Ve
.PP
Be careful: debugging output is voluminous and can generate several megabytes
of output.
.SH ATTENTION
.IX Header "ATTENTION"
Using <PTDEBUG> might expose passwords. When debug is enabled, all command line
parameters are shown in the output.
.SH "SYSTEM REQUIREMENTS"
.IX Header "SYSTEM REQUIREMENTS"
You need Perl, DBI, DBD::mysql, and some core packages that ought to be
installed in any reasonably new version of Perl.
.SH BUGS
.IX Header "BUGS"
For a list of known bugs, see <https://jira.percona.com/projects/PT/issues>.
.PP
Please report bugs at <https://jira.percona.com/projects/PT>.
Include the following information in your bug report:
.IP \(bu 4
Complete command-line used to run the tool
.IP \(bu 4
Tool "\-\-version"
.IP \(bu 4
MySQL version of all servers involved
.IP \(bu 4
Output from the tool including STDERR
.IP \(bu 4
Input files (log/dump/config files, etc.)
.PP
If possible, include debugging output by running the tool with \f(CW\*(C`PTDEBUG\*(C'\fR;
see "ENVIRONMENT".
.SH DOWNLOADING
.IX Header "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:
.PP
.Vb 1
\&   wget percona.com/get/percona\-toolkit.tar.gz
\&
\&   wget percona.com/get/percona\-toolkit.rpm
\&
\&   wget percona.com/get/percona\-toolkit.deb
.Ve
.PP
You can also get individual tools from the latest release:
.PP
.Vb 1
\&   wget percona.com/get/TOOL
.Ve
.PP
Replace \f(CW\*(C`TOOL\*(C'\fR with the name of any tool.
.SH AUTHORS
.IX Header "AUTHORS"
Baron Schwartz and Daniel Nichter
.SH "ABOUT PERCONA TOOLKIT"
.IX Header "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.
.SH "COPYRIGHT, LICENSE, AND WARRANTY"
.IX Header "COPYRIGHT, LICENSE, AND WARRANTY"
This program is copyright 2011\-2024 Percona LLC and/or its affiliates,
2007\-2011 Baron Schwartz.
.PP
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.
.PP
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.
.PP
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.
.SH VERSION
.IX Header "VERSION"
pt-duplicate-key-checker 3.7.0
.SH "POD ERRORS"
.IX Header "POD ERRORS"
Hey! \fBThe above document had some coding errors, which are explained below:\fR
.IP "Around line 5660:" 4
.IX Item "Around line 5660:"
Non-ASCII character seen before =encoding in 'Percona’s'. Assuming UTF\-8