Report a checksum for table contents. This statement calculates a value to compare tables, useful for verifying replication consistency.
CHECKSUM TABLE tbl_name [, tbl_name] ... [ QUICK | EXTENDED ]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 a replica).
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 returnsNULL 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 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:
CHECKSUM TABLE may give a different result as MariaDB doesn't ignore NULLs in the columns like 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 setting old_mode to COMPAT_5_1_CHECKSUM. Note, however, that the MyISAM and Aria storage engines in MariaDB are using the new checksum internally, so if you are using this old mode, the CHECKSUM command will be slower as it needs to calculate the checksum row by row.
You can get the 'old style' checksum in MariaDB by starting mariadbd with the --old option. Note, however, that the MyISAM and Aria storage engines in MariaDB are using the new checksum internally, so if you are using this old mode, the CHECKSUM command will be slower as it needs to calculate the checksum row by row.
This page is licensed: GPLv2, originally from fill_help_tables.sql
Last updated
Was this helpful?
Was this helpful?