MySQL Utilities 1.4 Manual  /  Manual Pages  /  mysqlindexcheck — Identify Potentially Redundant Table Indexes

5.11. mysqlindexcheck — Identify Potentially Redundant Table Indexes

This utility reads the indexes for one or more tables and identifies duplicate and potentially redundant indexes.

To check all tables in a database, only specify the database name. To check a specific table, name the table in db.table format. It is possible to mix database and table names.

You can scan tables in any database except the internal databases mysql, INFORMATION_SCHEMA, and performance_schema.

Depending on the index type, the utility applies the following rules to compare indexes (designated as idx_a and idx_b):

  • BTREE

    idx_b is redundant to idx_a if and only if the first n columns in idx_b also appear in idx_a. Order and uniqueness count.

  • HASH

    idx_a and idx_b are duplicates if and only if they contain the same columns in the same order. Uniqueness counts.

  • SPATIAL

    idx_a and idx_b are duplicates if and only if they contain the same column (only one column is permitted).

  • FULLTEXT

    idx_b is redundant to idx_a if and only if all columns in idx_b are included in idx_a. Order counts.

To see DROP statements drop redundant indexes, specify the --show-drops option. To examine the existing indexes, use the --verbose option, which prints the equivalent CREATE INDEX (or ALTER TABLE) for primary keys.

To display the best or worst non-primary key indexes for each table, use the --best or --worst option. This causes the output to show the best or worst indexes from tables with 10 or more rows. By default, each option shows five indexes. To override that, provide an integer value for the option.

To change the format of the index lists displayed for the --show-indexes, --best, and --worst options, use one of the following values with the --format option:

  • grid (default)

    Display output in grid or table format like that of the mysql client command-line tool.

  • csv

    Display output in comma-separated values format.

  • tab

    Display output in tab-separated format.

  • sql

    Print SQL statements rather than a list.

  • vertical

    Display output in single-column format like that of the \G command for the mysql client command-line tool.

Note

The --best and --worst lists cannot be printed as SQL statements.

OPTIONS

mysqlindexcheck accepts the following command-line options:

  • --help

    Display a help message and exit.

  • --license

    Display license information and exit.

  • --best[=<N>]

    If --stats is given, limit index statistics to the best N indexes. The default value of N is 5 if omitted.

  • --format=<index_format>, -f<index_format>

    Specify the index list display format for output produced by --stats. Permitted format values are grid, csv, tab, sql, and vertical. The default is grid.

  • --report-indexes, -r

    Reports if a table has neither UNIQUE indexes nor a PRIMARY key.

  • --server=<source>

    Connection information for the server.

    To connect to a server, it is necessary to specify connection parameters such as user name, host name, password, and either a port or socket. MySQL Utilities provides a number of ways to provide this information. All of the methods require specifying your choice via a command-line option such as --server, --master, --slave, etc. The methods include the following in order of most secure.

    • Use login-paths from your .mylogin.cnf file (encrypted, not visible). Example : <login-path>[:<port>][:<socket>]

    • Use a configuration file (unencrypted, not visible) Note: available in release-1.5.0. Example : <configuration-file-path>[:<section>]

    • Specify the data on the command-line (unencrypted, visible). Example : <user>[:<passwd>]@<host>[:<port>][:<socket>]

  • --show-drops, -d

    Display DROP statements for dropping indexes.

  • --show-indexes, -i

    Display indexes for each table.

  • --skip, -s

    Skip tables that do not exist.

  • --stats

    Show index performance statistics.

  • --verbose, -v

    Specify how much information to display. Use this option multiple times to increase the amount of information. For example, -v = verbose, -vv = more verbose, -vvv = debug.

  • --version

    Display version information and exit.

  • --worst[=<N>]

    If --stats is also passed in, limit index statistics to the worst N indexes. The default value of N is 5, if omitted.

NOTES

You must provide connection parameters (user, host, password, and so forth) for an account that has the appropriate privileges to read all objects accessed during the operation.

For the --format option, the permitted values are not case sensitive. In addition, values may be specified as any unambiguous prefix of a valid value. For example, --format=g specifies the grid format. An error occurs if a prefix matches more than one valid value.

The path to the MySQL client tools should be included in the PATH environment variable in order to use the authentication mechanism with login-paths. This will allow the utility to use the my_print_defaults tools which is required to read the login-path values from the login configuration file (.mylogin.cnf).

EXAMPLES

To check all tables in the employees database on the local server to see the possible redundant and duplicate indexes, use this command:

shell> mysqlindexcheck --server=root@localhost employees
# Source on localhost: ... connected.
# The following indexes are duplicates or redundant \
  for table employees.dept_emp:
#
CREATE INDEX emp_no ON employees.dept_emp (emp_no) USING BTREE
#     may be redundant or duplicate of:
ALTER TABLE employees.dept_emp ADD PRIMARY KEY (emp_no, dept_no)
# The following indexes are duplicates or redundant \
  for table employees.dept_manager:
#
CREATE INDEX emp_no ON employees.dept_manager (emp_no) USING BTREE
#     may be redundant or duplicate of:
ALTER TABLE employees.dept_manager ADD PRIMARY KEY (emp_no, dept_no)
# The following indexes are duplicates or redundant \
  for table employees.salaries:
#
CREATE INDEX emp_no ON employees.salaries (emp_no) USING BTREE
#     may be redundant or duplicate of:
ALTER TABLE employees.salaries ADD PRIMARY KEY (emp_no, from_date)
# The following indexes are duplicates or redundant \
  for table employees.titles:
#
CREATE INDEX emp_no ON employees.titles (emp_no) USING BTREE
#     may be redundant or duplicate of:
ALTER TABLE employees.titles ADD PRIMARY KEY (emp_no, title, from_date)

PERMISSIONS REQUIRED

Regarding the privileges needed to run this utility, the user needs SELECT privilege on the mysql database as well as for the databases which tables are being checked.


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