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

       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

       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:

       o   Read	the tool's documentation

       o   Review the tool's known "BUGS"

       o   Test	the tool on a non-production server

       o   Backup your production server and verify the	backups

       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.

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

	   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

	   Prompt for a	password when connecting to MySQL.

	   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.

	   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

	     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.

	   type: Array

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

	   short form: -d; type: hash

	   Check only this comma-separated list	of databases.

	   short form: -F; type: string

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

	   short form: -e; type: hash

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

	   Show	help and exit.

	   short form: -h; type: string

	   Connect to host.

	   type: Hash

	   Ignore this comma-separated list of databases.

	   type: Hash

	   Ignore this comma-separated list of storage engines.

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

	   type: Hash

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

	   type: string; default: fk

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

	   short form: -p; type: string

	   Password to use when	connecting.  If	password contains commas they
	   must	be escaped with	a backslash: "exam\,ple"

	   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.

	   short form: -P; type: int

	   Port	number to use for connection.

	   type: Array

	   Set the MySQL variables in this comma-separated list	of
	   "variable=value" pairs.

	   By default, the tool	sets:


	   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

	   short form: -S; type: string

	   Socket file to use for connection.

	   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".

	   default: yes

	   Print summary of indexes at end of output.

	   short form: -t; type: hash

	   Check only this comma-separated list	of tables.

	   Table names may be qualified	with the database name.

	   short form: -u; type: string

	   User	for login if not current user.

	   short form: -v

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

	   Show	version	and exit.

	   default: yes

	   Check for the latest	version	of Percona Toolkit, MySQL, and other

	   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 Perconaas 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

       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.

       o   A

	   dsn:	charset; copy: yes

	   Default character set.

       o   D

	   dsn:	database; copy:	yes

	   Default database.

       o   F

	   dsn:	mysql_read_default_file; copy: yes

	   Only	read default options from the given file

       o   h

	   dsn:	host; copy: yes

	   Connect to host.

       o   p

	   dsn:	password; copy:	yes

	   Password to use when	connecting.  If	password contains commas they
	   must	be escaped with	a backslash: "exam\,ple"

       o   P

	   dsn:	port; copy: yes

	   Port	number to use for connection.

       o   S

	   dsn:	mysql_socket; copy: yes

	   Socket file to use for connection.

       o   u

	   dsn:	user; copy: yes

	   User	for login if not current user.

       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.

       You need	Perl, DBI, DBD::mysql, and some	core packages that ought to be
       installed in any	reasonably new version of Perl.

       For a list of known bugs, see

       Please report bugs at <>.  Include
       the following information in your bug report:

       o   Complete command-line used to run the tool

       o   Tool	"--version"

       o   MySQL version of all	servers	involved

       o   Output from the tool	including STDERR

       o   Input files (log/dump/config	files, etc.)

       If possible, include debugging output by	running	the tool with
       "PTDEBUG"; see "ENVIRONMENT".

       Visit <>	to download
       the latest release of Percona Toolkit.  Or, get the latest release from
       the command line:




       You can also get	individual tools from the latest release:


       Replace "TOOL" with the name of any tool.

       Baron Schwartz and Daniel Nichter

       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 <> to learn
       about other free, open-source software from Percona.

       This program is copyright 2011-2018 Percona LLC and/or its affiliates,
       2007-2011 Baron Schwartz.


       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.

       pt-duplicate-key-checker	3.2.0

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

       Around line 5602:
	   Non-ASCII character seen before =encoding in	'Perconaas'. Assuming

perl v5.32.0			  2020-04-23	   PT-DUPLICATE-KEY-CHECKER(1)


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