The mysqlcheck client performs table maintenance: It checks, repairs, optimizes, and 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 12.3.5, “
LOCK TABLES and
TABLES Syntax”, for more information about
Table maintenance operations can be time-consuming, particularly
for large tables. If you use the
--all-databases option to process all tables in
one or more databases, an invocation of
mysqlcheck might take a long time.
mysqlcheck is available as of MySQL 3.23.38.
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 check or repair your tables.
mysqlcheck uses the SQL statements
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 12.4.2, “Table Maintenance Statements”.
MyISAM storage engine supports all four
maintenance operations, so mysqlcheck can be
used to perform any of them on
Other storage engines do not necessarily support all operations.
In such cases, an error message is displayed. For example, if
test.t is a
an attempt to check it produces this result:
mysqlcheck test ttest.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
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:
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
mysqlrepair, or make a symbolic link to
mysqlrepair. If you invoke
mysqlrepair, it repairs tables.
The names shown in the following table can be used to change mysqlcheck default behavior.
|mysqlrepair||The default option is |
|mysqlanalyze||The default option is |
|mysqloptimize||The default option is |
mysqlcheck supports the following options,
which can be specified on the command line or in the
option file groups. mysqlcheck also supports
the options for processing option files described at
Section 18.104.22.168.1, “Command-Line Options that Affect Option-File Handling”.
|--all-databases||Check all tables in all databases|
|--all-in-1||Execute a single statement for each database that names all the tables from that database|
|--analyze||Analyze the tables|
|--auto-repair||If a checked table is corrupted, automatically fix it|
|--character-sets-dir=path||Directory where character sets are installed|
|--check||Check the tables for errors|
|--check-only-changed||Check only tables that have changed since the last check|
|--compress||Compress all information sent between client and server|
|--databases||Process all tables in the named databases|
|--debug[=debug_options]||Write a debugging log|
|--default-character-set=charset_name||Specify 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|
|--extended||Check and repair tables|
|--fast||Check only tables that have not been closed properly|
|--force||Continue even if an SQL error occurs|
|--help||Display help message and exit|
|--host=host_name||Connect to MySQL server on given host|
|--medium-check||Do a check that is faster than an --extended operation|
|--no-defaults||Read no option files|
|--optimize||Optimize the tables|
|--password[=password]||Password to use when connecting to server|
|--pipe||On Windows, connect to server using named pipe|
|--port=port_num||TCP/IP port number to use for connection|
|--protocol=type||Connection protocol to use|
|--quick||The fastest method of checking|
|--repair||Perform a repair that can fix almost anything except unique keys that are not unique|
|--shared-memory-base-name=name||The name of shared memory to use for shared-memory connections|
|--socket=path||For connections to localhost, the Unix socket file to use|
|--ssl||Enable SSL for connection|
|--ssl-ca=file_name||Path of file that contains list of trusted SSL CAs|
|--ssl-capath=dir_name||Path of directory that contains trusted SSL CA certificates in PEM format|
|--ssl-cert=file_name||Path of file that contains X509 certificate in PEM format|
|--ssl-cipher=cipher_list||List of permitted ciphers to use for SSL encryption|
|--ssl-key=file_name||Path of file that contains X509 key in PEM format|
|--tables||Overrides the --databases or -B option|
|--use-frm||For repair operations on MyISAM tables|
|--user=user_name,||MySQL user name to use when connecting to server|
|--version||Display version information and exit|
Display a help message and exit.
Check all tables in all databases. This is the same as using
and naming all the databases on the command line.
Instead of issuing a statement for each table, execute a single statement for each database that names all the tables from that database to be processed.
Analyze the tables.
If a checked table is corrupted, automatically fix it. Any necessary repairs are done after all tables have been checked.
The directory where character sets are installed. See Section 9.6, “Character Set Configuration”.
Check the tables for errors. This is the default operation.
Check only tables that have changed since the last check or that have not been closed properly.
Compress all information sent between the client and the server if both support compression.
Process all tables in the named databases. Normally, mysqlcheck treats the first name argument on the command line as a database name and following names as table names. With this option, it treats all name arguments as database names.
Write a debugging log. A typical
debug_options string is
The default is
charset_name as the default
character set. See Section 9.6, “Character Set Configuration”.
If you are using this option to check tables, it ensures that they are 100% consistent but takes a long time.
If you are using this option to repair tables, it runs an extended repair that may not only take a long time to execute, but may produce a lot of garbage rows also!
Check only tables that have not been closed properly.
Continue even if an SQL error occurs.
Connect to the MySQL server on the given host.
Do a check that is faster than an
This finds only 99.99% of all errors, which should be good
enough in most cases.
Optimize the tables.
The password to use when connecting to the server. If you
use the short option form (
cannot have a space between the option
and the password. If you omit the
password value following the
-p option on the command line,
mysqlcheck prompts for one.
Specifying a password on the command line should be considered insecure. See Section 22.214.171.124, “End-User Guidelines for Password Security”. You can use an option file to avoid giving the password on the command line.
On Windows, connect to the server using a named pipe. This option applies only if the server supports named-pipe connections.
The TCP/IP port number to use for the connection.
The connection protocol to use for connecting to the server. It is useful when the other connection parameters normally would cause a protocol to be used other than the one you want. For details on the permissible values, see Section 4.2.2, “Connecting to the MySQL Server”. This option was added in MySQL 4.1.
If you are using this option to check tables, it prevents the check from scanning the rows to check for incorrect links. This is the fastest check method.
If you are using this option to repair tables, it tries to repair only the index tree. This is the fastest repair method.
Perform a repair that can fix almost anything except unique keys that are not unique.
Silent mode. Print only error messages.
For connections to
localhost, the Unix
socket file to use, or, on Windows, the name of the named
pipe to use.
-B option. All name arguments following
the option are regarded as table names.
For repair operations on
get the table structure from the
file so that the table can be repaired even if the
.MYI header is corrupted. This option
was added in MySQL 4.0.5.
The MySQL user name to use when connecting to the server.
Verbose mode. Print information about the various stages of program operation.
Display version information and exit.