MK-DUPLICATE-KEY-CHECKER(1)

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

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 the Sourceforge website at <http://sourceforge.net/projects/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

--allatonce
    Prints everything it finds in one chunk. The default is to print a database at a time.

--allstruct
    Compare indexes with different structures. 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.

--askpass
    Prompt for a password when connecting to MySQL.

--charset
    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.

--clustered
    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`)

--databases
    A comma-separated list of databases to examine.

--defaults-file
    Only read default options from the given file.

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

--function
    What to check: 'f' is foreign keys, 'k' is indexes. The default is to check both.

--help
    Displays a help message.

--host
    Connect to host.

--ignoredb
    A comma-separated list of databases to ignore.

--ignoreengine
    Use this option to skip a comma-separated list of storage engines (table types).

--ignoreorder
    Ignore column ordering, so an index on columns (a,b) is considered a duplicate of an index on columns (b,a).

--ignoretbl
    A comma-separated list of tables to ignore. Table names may be qualified with the database name.

--password
    Password to use when connecting.

--port
    Port number to use for connection.

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

--socket
    Socket file to use for connection.

--tab
    Print output separated with tabs, instead of whitespace-aligned. See "OUTPUT" for details.

--tables
    A comma-separated list of tables to check. Table names may be qualified with the database name.

--user
    User for login if not current user.

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

--version
    Output version information and exit.

OUTPUT
Output is to STDOUT, one line per server and table, with header lines for each database. I tried to make the output easy to process with awk. For this reason columns are always present. If there's no value, the script prints 'NULL'. Output is sorted by database and table.

The columns in the output are as follows.

DATABASE
    The database the table is in.

TABLE
    The table name.

ENGINE
    The table's storage engine.

OBJECT
    The index or constraint's name, e.g. `tbl_ibfk_3` (the default InnoDB name for the third foreign key on a table named tbl).

TYPE
    'KEY' for indexes, 'FK' for foreign keys.

STRUCT
    The type of index: BTREE, FULLTEXT, HASH etc. By default MySQL's indexes are BTREE in most cases. This does not apply to foreign keys.

PARENT
    The parent table to which the foreign key constraint refers. This does not apply to indexes.

COLUMNS
    The columns included in the index or foreign key constraint. For indexes, this column list is output verbatim, as shown in SHOW CREATE TABLE. For foreign keys, the columns are ordered so string comparison can find duplicates, since column order in a foreign key is immaterial.

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 the Sourceforge bug tracker, forums, and mailing lists to request support or report bugs: <http://sourceforge.net/projects/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 (c) 2007 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.

VERSION
This manual page documents Ver 1.1.6 Distrib 1972 $Revision: 1970 $.