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The mysqlcheck client checks, repairs, optimizes, and analyzes tables.
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 Chapter 13, SQL Statement Syntax.
MyISAM storage engine supports all four statements, so mysqlcheck can be used to perform all four operations 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:
mysqlcheck test ttest.t note : The storage engine for the table doesn't support check
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 filesystem errors.
There are three general ways to invoke mysqlcheck:
If you do not name any tables following
db_name or if you use the
--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 following names 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:
Display a help message and exit.
Check all tables in all databases. This is the same as using the
--databases option 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.
MySQL Enterprise. For expert advice on optimizing tables, subscribe to the MySQL Network Monitoring and Advisory Service. For more information see http://www.mysql.com/products/enterprise/advisors.html.
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 5.10.1, “The Character Set Used for Data and Sorting”.
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.
CHECK TABLE with the
FOR UPGRADE option to check tables for incompatibilities with the current version of the server. This option was added in MySQL 5.0.19.
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 often
charset_name as the default character set. See Section 5.10.1, “The Character Set Used for Data and Sorting”.
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
--extended operation. 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 (
-p), you cannot have a space between the option and the password. If you omit the
password value following the
-p option on the command line, you are prompted for one.
Specifying a password on the command line should be considered insecure. See Section 5.8.6, “Keeping Your Password Secure”.
The TCP/IP port number to use for the connection.
The connection protocol to use.
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.
Options that begin with
--ssl specify whether to connect to the server via SSL and indicate where to find SSL keys and certificates. See Section 126.96.36.199, “SSL Command Options”.
-B option. All name arguments following the option are regarded as table names.
For repair operations on
MyISAM tables, get the table structure from the
.frm file so that the table can be repaired even if the
.MYI header is corrupted.
The MySQL username to use when connecting to the server.
Verbose mode. Print information about the various stages of program operation.
Display version information and exit.
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