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PROGRAM:

NAME

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

SYNOPSIS

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

RISKS

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:

· Read the tool's documentation

· Review the tool's known "BUGS"

· Test the tool on a non-production server

· Backup your production server and verify the backups

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.

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.

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. If password contains commas they must be escaped
with a backslash: "exam\,ple"

--pid
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.

--port
short form: -P; type: int

Port number to use for connection.

--set-vars
type: Array

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

By default, the tool sets:

wait_timeout=10000

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 set.

--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.

--[no]version-check
default: yes

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

This is a standard "check for updates automatically" feature, with two additional
features. First, the tool checks the version of other programs on the local system in
addition to its own version. For example, it checks the version of every MySQL server
it connects to, Perl, and the Perl module DBD::mysql. 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.

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 <https://www.percona.com/version-check>.

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. If password contains commas they must be escaped
with a backslash: "exam\,ple"

· 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.

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