NAME¶
pt-duplicate-key-checker - Find duplicate indexes and foreign keys on MySQL
tables.
SYNOPSIS¶
Usage: pt-duplicate-key-checker [OPTION...] [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¶
The following section is included to inform users about the potential risks,
whether known or unknown, of using this tool. The two main categories of risks
are those created by the nature of the tool (e.g. read-only tools vs.
read-write tools) and those created by bugs.
pt-duplicate-key-checker is a read-only tool that executes SHOW CREATE TABLE and
related queries to inspect table structures, and thus is very low-risk.
At the time of this release, there is an unconfirmed bug that causes the tool to
crash.
The authoritative source for updated information is always the online issue
tracking system. Issues that affect this tool will be marked as such. You can
see a list of such issues at the following URL:
http://www.percona.com/bugs/pt-duplicate-key-checker
<
http://www.percona.com/bugs/pt-duplicate-key-checker>.
See also "BUGS" for more information on filing bugs and getting help.
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.
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.
- --pid
- type: string
Create the given PID file. The file contains the process ID of the script.
The PID file is removed when the script exits. Before starting, the script
checks if the PID file already exists. If it does not, then the script
creates and writes its own PID to it. If it does, then the script checks
the following: if the file contains a PID and a process is running with
that PID, then the script dies; or, if there is no process running with
that PID, then the script overwrites the file with its own PID and starts;
else, if the file contains no PID, then the script dies.
- --port
- short form: -P; type: int
Port number to use for connection.
- --set-vars
- type: string; default: wait_timeout=10000
Set these MySQL variables. Immediately after connecting to MySQL, this
string will be appended to SET and executed.
- --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.
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.
- •
- 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
<
http://www.percona.com/bugs/pt-duplicate-key-checker>.
Please report bugs at
https://bugs.launchpad.net/percona-toolkit
<
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/
<
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
This tool is part of Percona Toolkit, a collection of advanced command-line
tools developed by Percona for MySQL support and consulting. Percona Toolkit
was forked from two projects in June, 2011: Maatkit and Aspersa. Those
projects were created by Baron Schwartz and developed primarily by him and
Daniel Nichter, both of whom are employed by Percona. Visit
<
http://www.percona.com/software/> for more software developed by
Percona.
COPYRIGHT, LICENSE, AND WARRANTY¶
This program is copyright 2007-2011 Baron Schwartz, 2011-2012 Percona Inc.
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
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 2.1.2