5.9.4.6. Setting Up a Table Maintenance Schedule
It is a good idea to perform table checks on a regular basis
rather than waiting for problems to occur. One way to check
and repair MyISAM tables is with the
CHECK TABLE and REPAIR
TABLE statements. See Section 13.5.2.3, “CHECK TABLE Syntax”,
and Section 13.5.2.6, “REPAIR TABLE Syntax”.
Another way to check tables is to use
myisamchk. For maintenance purposes, you
can use myisamchk -s. The
-s option (short for
--silent) causes myisamchk
to run in silent mode, printing messages only when errors
occur.
It is also a good idea to enable automatic
MyISAM table checking. For example,
whenever the machine has done a restart in the middle of an
update, you usually need to check each table that could have
been affected before it is used further. (These are
“expected crashed tables.”) To check
MyISAM tables automatically, start the
server with the --myisam-recover option. See
Section 5.2.1, “mysqld Command Options”.
You should also check your tables regularly during normal
system operation. At MySQL AB, we run a
cron job to check all our important tables
once a week, using a line like this in a
crontab file:
35 0 * * 0 /path/to/myisamchk --fast --silent /path/to/datadir/*/*.MYI
This prints out information about crashed tables so that we
can examine and repair them when needed.
Because we have not had any unexpectedly crashed tables
(tables that become corrupted for reasons other than hardware
trouble) for several years, once a week is more than
sufficient for us.
We recommend that to start with, you execute
myisamchk -s each night on all tables that
have been updated during the last 24 hours, until you come to
trust MySQL as much as we do.
Normally, MySQL tables need little maintenance. If you are
performing many updates to MyISAM tables
with dynamic-sized rows (tables with
VARCHAR, BLOB, or
TEXT columns) or have tables with many
deleted rows you may want to defragment/reclaim space from the
tables from time to time. You can do this by using
OPTIMIZE TABLE on the tables in question.
Alternatively, if you can stop the mysqld
server for a while, change location into the data directory
and use this command while the server is stopped:
shell> myisamchk -r -s --sort-index --sort_buffer_size=16M */*.MYI
