14.1.4.1. Corrupted MyISAM Tables
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).
Hardware failures.
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 MyISAM
code.
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 MyISAM table
using the 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 13.5.2.3, “CHECK TABLE Syntax”,
Section 13.5.2.6, “REPAIR TABLE Syntax”, and
Section 8.2, “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 a
server crash. 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 A.4.2, “What to Do If MySQL Keeps Crashing”, and
Section E.1.6, “Making a Test Case If You Experience Table Corruption”.
