The following options to mysqld can be used
to change the behavior of MyISAM
tables. For
additional information, see Section 5.1.2, “Server Command Options”.
Set the mode for automatic recovery of crashed
MyISAM
tables.
Don't flush key buffers between writes for any
MyISAM
table.
If you do this, you should not access
MyISAM
tables from another program
(such as from another MySQL server or with
myisamchk) when the tables are in use.
Doing so risks index corruption. Using
--external-locking
does not
eliminate this risk.
The following system variables affect the behavior of
MyISAM
tables. For additional information,
see Section 5.1.3, “Server System Variables”.
The size of the tree cache used in bulk insert optimization.
This is a limit per thread!
myisam_max_extra_sort_file_size
Used to help MySQL to decide when to use the slow but safe key cache index creation method.
This parameter is given in megabytes before MySQL 4.0.3, and in bytes as of 4.0.3.
The maximum size of the temporary file that MySQL is allowed
to use while re-creating a MyISAM
index
(during REPAIR TABLE
,
ALTER TABLE
, or
LOAD DATA
INFILE
). If the file size would be larger than
this value, the index is created using the key cache
instead, which is slower. This variable was added in MySQL
3.23.37.
The value is given in megabytes before 4.0.3 and in bytes thereafter.
Set the size of the buffer used when recovering tables.
Automatic recovery is activated if you start
mysqld with the
--myisam-recover
option. In this
case, when the server opens a MyISAM
table,
it checks whether the table is marked as crashed or whether the
open count variable for the table is not 0 and you are running
the server with external locking disabled. If either of these
conditions is true, the following happens:
The server checks the table for errors.
If the server finds an error, it tries to do a fast table repair (with sorting and without re-creating the data file).
If the repair fails because of an error in the data file (for example, a duplicate-key error), the server tries again, this time re-creating the data file.
If the repair still fails, the server tries once more with the old repair option method (write row by row without sorting). This method should be able to repair any type of error and has low disk space requirements.
MySQL Enterprise.
Subscribers to MySQL Enterprise Monitor receive notification
if the --myisam-recover
option
has not been set. For more information, see
http://www.mysql.com/products/enterprise/advisors.html.
If the recovery wouldn't be able to recover all rows from
previously completed statements and you didn't specify
FORCE
in the value of the
--myisam-recover
option,
automatic repair aborts with an error message in the error log:
Error: Couldn't repair table: test.g00pages
If you specify FORCE
, a warning like this is
written instead:
Warning: Found 344 of 354 rows when repairing ./test/g00pages
Note that if the automatic recovery value includes
BACKUP
, the recovery process creates files
with names of the form
.
You should have a cron script that
automatically moves these files from the database directories to
backup media.
tbl_name-datetime
.BAK
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