4.5.3 mysqlcheck — A Table Maintenance Program

The mysqlcheck client performs table maintenance: It checks, repairs, optimizes, or analyzes tables.

Each table is locked and therefore unavailable to other sessions while it is being processed, although for check operations, the table is locked with a READ lock only (see Section 13.3.5, “LOCK TABLES and UNLOCK TABLES Syntax”, for more information about READ and WRITE locks). Table maintenance operations can be time-consuming, particularly for large tables. If you use the --databases or --all-databases option to process all tables in one or more databases, an invocation of mysqlcheck might take a long time. (This is also true for mysql_upgrade because that program invokes mysqlcheck to check all tables and repair them if necessary.)

mysqlcheck is similar in function to myisamchk, but works differently. The main operational difference is that mysqlcheck must be used when the mysqld server is running, whereas myisamchk should be used when it is not. The benefit of using mysqlcheck is that you do not have to stop the server to perform table maintenance.

mysqlcheck uses the SQL statements CHECK TABLE, REPAIR TABLE, ANALYZE TABLE, and OPTIMIZE TABLE in a convenient way for the user. It determines which statements to use for the operation you want to perform, and then sends the statements to the server to be executed. For details about which storage engines each statement works with, see the descriptions for those statements in Section 13.7.2, “Table Maintenance Statements”.

The MyISAM storage engine supports all four maintenance operations, so mysqlcheck can be used to perform any of them on MyISAM tables. Other storage engines do not necessarily support all operations. In such cases, an error message is displayed. For example, if test.t is a MEMORY table, an attempt to check it produces this result:

shell> mysqlcheck test t
test.t
note     : The storage engine for the table doesn't support check

If mysqlcheck is unable to repair a table, see Section 2.11.4, “Rebuilding or Repairing Tables or Indexes” for manual table repair strategies. This will be the case, for example, for InnoDB tables, which can be checked with CHECK TABLE, but not repaired with REPAIR TABLE.

Caution

It is best to make a backup of a table before performing a table repair operation; under some circumstances the operation might cause data loss. Possible causes include but are not limited to file system errors.

There are three general ways to invoke mysqlcheck:

shell> mysqlcheck [options] db_name [tbl_name ...]
shell> mysqlcheck [options] --databases db_name ...
shell> mysqlcheck [options] --all-databases

If you do not name any tables following db_name or if you use the --databases or --all-databases option, entire databases are checked.

mysqlcheck has a special feature compared to other client programs. The default behavior of checking tables (--check) can be changed by renaming the binary. If you want to have a tool that repairs tables by default, you should just make a copy of mysqlcheck named mysqlrepair, or make a symbolic link to mysqlcheck named mysqlrepair. If you invoke mysqlrepair, it repairs tables.

The names shown in the following table can be used to change mysqlcheck default behavior.

CommandMeaning
mysqlrepairThe default option is --repair
mysqlanalyzeThe default option is --analyze
mysqloptimizeThe default option is --optimize

mysqlcheck supports the following options, which can be specified on the command line or in the [mysqlcheck] and [client] groups of an option file. For information about option files, see Section 4.2.6, “Using Option Files”.

Table 4.7 mysqlcheck Options

FormatOption FileDescriptionIntroduced
--all-databasesall-databasesCheck all tables in all databases 
--all-in-1all-in-1Execute a single statement for each database that names all the tables from that database 
--analyzeanalyzeAnalyze the tables 
--auto-repairauto-repairIf a checked table is corrupted, automatically fix it 
--character-sets-dir=pathcharacter-sets-dirDirectory where character sets are installed 
--checkcheckCheck the tables for errors 
--check-only-changedcheck-only-changedCheck only tables that have changed since the last check 
--check-upgradecheck-upgradeInvoke CHECK TABLE with the FOR UPGRADE option 
--compresscompressCompress all information sent between client and server 
--databasesdatabasesProcess all tables in the named databases 
--debug[=debug_options]debugWrite a debugging log 
--debug-checkdebug-checkPrint debugging information when program exits 
--debug-infodebug-infoPrint debugging information, memory, and CPU statistics when program exits 
--default-auth=plugindefault-auth=pluginAuthentication plugin to use5.5.10
--default-character-set=charset_namedefault-character-setSpecify default character set 
--defaults-extra-file=file_name Read option file in addition to usual option files 
--defaults-file=file_name Read only named option file 
--defaults-group-suffix=str Option group suffix value 
--extendedextendedCheck and repair tables 
--fastfastCheck only tables that have not been closed properly 
--fix-db-namesfix-db-namesConvert database names to 5.1 format 
--fix-table-namesfix-table-namesConvert table names to 5.1 format 
--forceforceContinue even if an SQL error occurs 
--help Display help message and exit 
--host=host_namehostConnect to MySQL server on given host 
--medium-checkmedium-checkDo a check that is faster than an --extended operation 
--no-defaults Read no option files 
--optimizeoptimizeOptimize the tables 
--password[=password]passwordPassword to use when connecting to server 
--pipepipeOn Windows, connect to server using named pipe 
--plugin-dir=pathplugin-dir=pathDirectory where plugins are installed5.5.10
--port=port_numportTCP/IP port number to use for connection 
--print-defaults Print defaults 
--protocol=typeprotocolConnection protocol to use 
--quickquickThe fastest method of checking 
--repairrepairPerform a repair that can fix almost anything except unique keys that are not unique 
--shared-memory-base-name=nameshared-memory-base-nameThe name of shared memory to use for shared-memory connections 
--silentsilentSilent mode 
--socket=pathsocketFor connections to localhost, the Unix socket file to use 
--sslsslEnable SSL for connection 
--ssl-ca=file_namessl-caPath of file that contains list of trusted SSL CAs 
--ssl-capath=dir_namessl-capathPath of directory that contains trusted SSL CA certificates in PEM format 
--ssl-cert=file_namessl-certPath of file that contains X509 certificate in PEM format 
--ssl-cipher=cipher_listssl-cipherList of permitted ciphers to use for SSL encryption 
--ssl-key=file_namessl-keyPath of file that contains X509 key in PEM format 
--ssl-verify-server-certssl-verify-server-certVerify server Common Name value in its certificate against host name used when connecting to server 
--tablestablesOverrides the --databases or -B option 
--use-frmuse-frmFor repair operations on MyISAM tables 
--user=user_name,userMySQL user name to use when connecting to server 
--verbose Verbose mode 
--version Display version information and exit 
--write-binlogwrite-binlogLog ANALYZE, OPTIMIZE, REPAIR statements to binary log. --skip-write-binlog adds NO_WRITE_TO_BINLOG to these statements.