Skip navigation links
13.1.2 Space Needed for Keys »
Section Navigation      [Toggle]

13.1.1. MyISAM Startup Options

The following options to mysqld can be used to change the behavior of MyISAM tables. For additional information, see Section 5.1.2, “Server Command Options”.

  • --myisam-recover=mode

    Set the mode for automatic recovery of crashed MyISAM tables.

  • --delay-key-write=ALL

    Don't flush key buffers between writes for any MyISAM table.

    Note

    If you do this, you should not access MyISAM tables from another program (such as from another MySQL server or with myisamchk) when the tables are in use. Doing so risks index corruption. Using --external-locking does not eliminate this risk.

The following system variables affect the behavior of MyISAM tables. For additional information, see Section 5.1.3, “Server System Variables”.

  • bulk_insert_buffer_size

    The size of the tree cache used in bulk insert optimization.

    Note

    This is a limit per thread!

  • myisam_max_extra_sort_file_size

    Used to help MySQL to decide when to use the slow but safe key cache index creation method.

    Note

    This parameter is given in megabytes before MySQL 4.0.3, and in bytes as of 4.0.3.

  • myisam_max_sort_file_size

    The maximum size of the temporary file that MySQL is allowed to use while re-creating a MyISAM index (during REPAIR TABLE, ALTER TABLE, or LOAD DATA INFILE). If the file size would be larger than this value, the index is created using the key cache instead, which is slower. This variable was added in MySQL 3.23.37.

    Note

    The value is given in megabytes before 4.0.3 and in bytes thereafter.

  • myisam_sort_buffer_size

    Set the size of the buffer used when recovering tables.

Automatic recovery is activated if you start mysqld with the --myisam-recover option. In this case, when the server opens a MyISAM table, it checks whether the table is marked as crashed or whether the open count variable for the table is not 0 and you are running the server with external locking disabled. If either of these conditions is true, the following happens:

  • The server checks the table for errors.

  • If the server finds an error, it tries to do a fast table repair (with sorting and without re-creating the data file).

  • If the repair fails because of an error in the data file (for example, a duplicate-key error), the server tries again, this time re-creating the data file.

  • If the repair still fails, the server tries once more with the old repair option method (write row by row without sorting). This method should be able to repair any type of error and has low disk space requirements.

MySQL Enterprise.  Subscribers to MySQL Enterprise Monitor receive notification if the --myisam-recover option has not been set. For more information, see http://www.mysql.com/products/enterprise/advisors.html.

If the recovery wouldn't be able to recover all rows from previously completed statements and you didn't specify FORCE in the value of the --myisam-recover option, automatic repair aborts with an error message in the error log: 

Error: Couldn't repair table: test.g00pages

If you specify FORCE, a warning like this is written instead: 

Warning: Found 344 of 354 rows when repairing ./test/g00pages

Note that if the automatic recovery value includes BACKUP, the recovery process creates files with names of the form tbl_name-datetime.BAK. You should have a cron script that automatically moves these files from the database directories to backup media.