Provided by: percona-toolkit_2.2.16-1_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 the version of other programs on the local system in
addition to its own version. For example, it checks the version of every MySQL server
it connects to, Perl, and the Perl module DBD::mysql. 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.
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/version-check>.
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://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 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 2011-2015 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 2.2.16