Man page for mk-duplicate-key-checker

August 24, 2007 – 5:35 pm

MK-DUPLICATE-KEY-CHECKER

Section: User Contributed Perl Documentation (1)
Updated: 2008-06-01
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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 $.

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