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Corrupted My i sam Tables

Even though the My ISAM table format is very reliable (all changes to a table madę 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 My ISAM codę.

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 dont find rows in the table or return incomplete results.

You can check the health of a My ISAM table using the CHECK TABLE statement, and repair a

corrupted My ISAM table with REPAIR TABLE. When mysqld is not running, you can also check

or repair a table with the myisamchk command. See Section 13.7.2.2, "CHECK TABLE Syntax”,

Section 13.7.2.5, “REPAIR TABLE Syntax", and Section 4.6.3, “myisamchk — MylSAM 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 C.5.4.2, “What to Do If MySQL Keeps Crashing", and

MySQL Internals: Porting to Other Systems.