Using myisamchk for Crash Recovery in cPnael
If you run mysqld with external locking disabled (which is the default), you cannot reliably use myisamchk to check a table when mysqld is using the same table.
If the server is run with external locking enabled, you can use myisamchk to check tables at any time. In this case, if the server tries to update a table that myisamchk is using, the server will wait for myisamchk to finish before it continues.
If you use myisamchk to repair or optimize tables, you must always ensure that the mysqld server is not using the table (this also applies if external locking is disabled). If you do not stop mysqld, you should at least do a mysqladmin flush-tables before you run myisamchk. Your tables may become corrupted if the server and myisamchk access the tables simultaneously.
When performing crash recovery, it is important to understand that each MyISAM table tbl_name in a database corresponds to the three files in the database directory shown in the following table.
tbl_name.frm Definition (format) file
tbl_name.MYD Data file
tbl_name.MYI Index file
Each of these three file types is subject to corruption in various ways, but problems occur most often in data files and index files.
myisamchk works by creating a copy of the .MYD data file row by row. It ends the repair stage by removing the old .MYD file and renaming the new file to the original file name.
This does a complete and thorough check of all data (-e means “extended check”). It does a check-read of every key for each row to verify that they indeed point to the correct row. This may take a long time for a large table that has many indexes. Normally, myisamchk stops after the first error it finds. If you want to obtain more information, you can add the -v (verbose) option. This causes myisamchk to keep going, up through a maximum of 20 errors.
Reference: http://dev.mysql.com/
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