Corrupted MyISAM Tables-opracowanie

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 13.7.2.2, “CHECK TABLE Syntax”,
Section 13.7.2.5, “REPAIR TABLE Syntax”, 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 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.
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