The Ultimate Guide to High Availability with MariaDB
This is a read-only copy of the MariaDB Knowledgebase generated on 2024-11-21. For the latest, interactive version please visit https://mariadb.com/kb/.

CHECKSUM TABLE

Syntax

CHECKSUM TABLE tbl_name [, tbl_name] ... [ QUICK | EXTENDED ]

Contents

  1. Syntax
  2. Description
  3. Identical Tables
  4. Differences Between MariaDB and MySQL

Description

CHECKSUM TABLE reports a table checksum. This is very useful if you want to know if two tables are the same (for example on a master and slave).

With QUICK, the live table checksum is reported if it is available, or NULL otherwise. This is very fast. A live checksum is enabled by specifying the CHECKSUM=1 table option when you create the table; currently, this is supported only for Aria and MyISAM tables.

With EXTENDED, the entire table is read row by row and the checksum is calculated. This can be very slow for large tables.

If neither QUICK nor EXTENDED is specified, MariaDB returns a live checksum if the table storage engine supports it and scans the table otherwise.

CHECKSUM TABLE requires the SELECT privilege for the table.

For a nonexistent table, CHECKSUM TABLE returns NULL and generates a warning.

The table row format affects the checksum value. If the row format changes, the checksum will change. This means that when a table created with a MariaDB/MySQL version is upgraded to another version, the checksum value will probably change.

Two identical tables should always match to the same checksum value; however, also for non-identical tables there is a very slight chance that they will return the same value as the hashing algorithm is not completely collision-free.

Identical Tables

Identical tables mean that the CREATE statement is identical and that the following variable, which affects the storage formats, was the same when the tables were created:

Differences Between MariaDB and MySQL

CHECKSUM TABLE may give a different result as MariaDB doesn't ignore NULLs in the columns as MySQL 5.1 does (Later MySQL versions should calculate checksums the same way as MariaDB). You can get the 'old style' checksum in MariaDB by starting mysqld with the --old option. Note however that that the MyISAM and Aria storage engines in MariaDB are using the new checksum internally, so if you are using --old, the CHECKSUM command will be slower as it needs to calculate the checksum row by row. Starting from MariaDB Server 10.9, --old is deprecated and will be removed in a future release. Set --old-mode or OLD_MODE to COMPAT_5_1_CHECKSUM to get 'old style' checksum.

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