MySQL :: MySQL 8.4 Reference Manual :: 18.2.1 MyISAM Startup Options (original) (raw)

18.2.1 MyISAM Startup Options

The following options to mysqld can be used to change the behavior of MyISAM tables. For additional information, see Section 7.1.7, “Server Command Options”.

The following system variables affect the behavior ofMyISAM tables. For additional information, seeSection 7.1.8, “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!
• delay_key_write=ALL
  Don't flush key buffers between writes for anyMyISAM table.
  Note
  If you do this, you should not accessMyISAM tables from another program (such as from another MySQL server or withmyisamchk) when the tables are in use. Doing so risks index corruption. Using--external-locking does not eliminate this risk.
• myisam_max_sort_file_size
  The maximum size of the temporary file that MySQL is permitted to use while re-creating a MyISAM index (during REPAIR TABLE,ALTER TABLE, orLOAD DATA). If the file size would be larger than this value, the index is created using the key cache instead, which is slower. The value is given in bytes.
• myisam_recover_options=mode
  Set the mode for automatic recovery of crashedMyISAM tables.
• myisam_sort_buffer_size
  Set the size of the buffer used when recovering tables.

Automatic recovery is activated if you startmysqld with themyisam_recover_options system variable set. In this case, when the server opens aMyISAM 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.

If the recovery wouldn't be able to recover all rows from previously completed statements and you didn't specifyFORCE in the value of themyisam_recover_options system variable, 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

If the automatic recovery value includesBACKUP, the recovery process creates files with names of the form_`tblname-datetime`_.BAK. You should have a cron script that automatically moves these files from the database directories to backup media.