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mk-duplicate-key-checker.1p

NAME

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

SYNOPSIS

    mk-duplicate-key-checker --host host1
 
 

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 colums. 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.

DOWNLOADING

You can download Maatkit from Google Code at <http://code.google.com/p/maatkit/>, or you can get any of the tools easily with a command like the following:

    wget http://www.maatkit.org/get/toolname
    or
    wget http://www.maatkit.org/trunk/toolname
 
 

Where "toolname" can be replaced with the name (or fragment of a name) of any of the Maatkit tools. Once downloaded, they're ready to run; no installation is needed. The first URL gets the latest released version of the tool, and the second gets the latest trunk code from Subversion.

OPTIONS

--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.

Enables character set settings in Perl and MySQL. 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 "a" and also remove the ORDER BY, the query should return the same results.

Currently, the tool suggests removing these indexes, but it should suggest shortening them instead. This is filed as a feature request (issue 295).

--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

Do only tables whose storage engine is in this comma-separated list.

--key-types

type: string; default: fk

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

--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.

--password

short form: -p; type: string

Password to use when connecting.

--port

short form: -P; type: int

Port number to use for connection.

--set-vars

type: string

Set these MySQL variables (default wait_timeout=10000).

Specify any variables you want to be set immediately after connecting to MySQL. These will be included in a "SET" command.

--socket

short form: -S; type: string

Socket file to use for connection.

--[no]summary

default: yes

Print summary of indexes at end of output.

--[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 --nosql.

--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.

ENVIRONMENT

The environment variable "MKDEBUG" enables verbose debugging output in all of the Maatkit tools:

    MKDEBUG=1 mk-....
 
 

SYSTEM REQUIREMENTS

You need the following Perl modules: DBI and DBD::mysql.

BUGS

Please use Google Code Issues and Groups to report bugs or request support: <http://code.google.com/p/maatkit/>.

Please include the complete command-line used to reproduce the problem you are seeing, the version of all MySQL servers involved, the complete output of the tool when run with ``--version'', and if possible, debugging output produced by running with the "MKDEBUG=1" environment variable.

LICENSE

This program is copyright 2007-2009 Baron Schwartz. Feedback and improvements are welcome.

THIS PROGRAM IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTIBILITY 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.

AUTHOR

Baron Schwartz, Daniel Nichter

VERSION

This manual page documents Ver 1.2.3 Distrib 3519 $Revision: 3502 $.