Even though the
MyISAM table format is very
reliable (all changes to a table made by an SQL statement are
written before the statement returns), you can still get
corrupted tables if any of the following events occur:
The mysqld process is killed in the middle of a write.
An unexpected computer shutdown occurs (for example, the computer is turned off).
You are using an external program (such as myisamchk) to modify a table that is being modified by the server at the same time.
A software bug in the MySQL or
Typical symptoms of a corrupt table are:
You get the following error while selecting data from the table:
Incorrect key file for table: '...'. Try to repair it
Queries don't find rows in the table or return incomplete results.
You can check the health of a
CHECK TABLE statement,
and repair a corrupted
MyISAM table with
REPAIR TABLE. When
mysqld is not running, you can also check or
repair a table with the myisamchk command.
See Section 18.104.22.168, “CHECK TABLE Statement”,
Section 22.214.171.124, “REPAIR TABLE Statement”, and Section 4.6.3, “myisamchk — MyISAM Table-Maintenance Utility”.
If your tables become corrupted frequently, you should try to
determine why this is happening. The most important thing to
know is whether the table became corrupted as a result of an
unexpected server exit. You can verify this easily by looking
for a recent
restarted mysqld message in the
error log. If there is such a message, it is likely that table
corruption is a result of the server dying. Otherwise,
corruption may have occurred during normal operation. This is a
bug. You should try to create a reproducible test case that
demonstrates the problem. See Section B.3.3.3, “What to Do If MySQL Keeps Crashing”, and
Section 5.8, “Debugging MySQL”.