(mysql.info) crash-recovery

 
 5.10.4.1 Using `myisamchk' for Crash Recovery
 .............................................
 
 This section describes how to check for and deal with data corruption
 in MySQL databases. If your tables become corrupted frequently, you
 should try to find the reason why. See  crashing.
 
 For an explanation of how `MyISAM' tables can become corrupted, see
  myisam-table-problems.
 
 If you run `mysqld' with external locking disabled (which is the
 default as of MySQL 4.0), you cannot reliably use `myisamchk' to check
 a table when `mysqld' is using the same table. If you can be certain
 that no one will access the tables through `mysqld' while you run
 `myisamchk', you only have to execute `mysqladmin flush-tables' before
 you start checking the tables. If you cannot guarantee this, you must
 stop `mysqld' while you check the tables. If you run `myisamchk' to
 check tables that `mysqld' is updating at the same time, you may get a
 warning that a table is corrupt even when it is not.
 
 If the server is run with external locking enabled, you can use
 `myisamchk' to check tables at any time.  In this case, if the server
 tries to update a table that `myisamchk' is using, the server will wait
 for `myisamchk' to finish before it continues.
 
 If you use `myisamchk' to repair or optimize tables, you _must_ always
 ensure that the `mysqld' server is not using the table (this also
 applies if external locking is disabled). If you don't stop `mysqld',
 you should at least do a `mysqladmin flush-tables' before you run
 `myisamchk'. Your tables _may become corrupted_ if the server and
 `myisamchk' access the tables simultaneously.
 
 When performing crash recovery, it is important to understand that each
 `MyISAM' table TBL_NAME in a database corresponds to three files in the
 database directory:
 
 *File*         *Purpose*
 `TBL_NAME.frm' Definition (format) file
 `TBL_NAME.MYD' Data file
 `TBL_NAME.MYI' Index file
 
 Each of these three file types is subject to corruption in various
 ways, but problems occur most often in data files and index files.
 
 `myisamchk' works by creating a copy of the `.MYD' data file row by
 row. It ends the repair stage by removing the old `.MYD' file and
 renaming the new file to the original file name. If you use -quick,
 `myisamchk' does not create a temporary `.MYD' file, but instead
 assumes that the `.MYD' file is correct and generates only a new index
 file without touching the `.MYD' file. This is safe, because
 `myisamchk' automatically detects whether the `.MYD' file is corrupt
 and aborts the repair if it is. You can also specify the -quick option
 twice to `myisamchk'. In this case, `myisamchk' does not abort on some
 errors (such as duplicate-key errors) but instead tries to resolve them
 by modifying the `.MYD' file. Normally the use of two -quick options is
 useful only if you have too little free disk space to perform a normal
 repair. In this case, you should at least make a backup of the table
 before running `myisamchk'.
Info Catalog
(mysql.info) table-maintenance
(mysql.info) check
automatically generated byinfo2html