13.4 Utiliser isamchk pour réparer une table

The file format that MySQL uses to store data has been extensively tested, but there are always external circumstances that may cause database tables to become corrupted:

• The mysqld process being killed in the middle of a write
• Unexpected shutdown of the computer (for example, if the computer is turned off)
• A hardware error

This chapter describes how to check for and deal with data corruption in MySQL databases. If your tables get corrupted a lot you should try to find the reason for this! G.1 Debugguer un serveur MySQL.

When performing crash recovery, it is important to understand that each table nom_table in a database corresponds to three files in the database directory:

Each of these three file types is subject to corruption in various ways, but problems occur most often in data files and index files.

isamchk works by creating a copy of the `.ISD' (data) file row by row. It ends the repair stage by removing the old `.ISD' file and renaming the new file to the original file name. If you use --quick, isamchk does not create a temporary `.ISD' file, but instead assumes that the `.ISD' file is correct and only generates a new index file without touching the `.ISD' file. This is safe, because isamchk automatically detects if the `.ISD' file is corrupt and aborts the repair in this case. You can also give two --quick options to isamchk. In this case, isamchk does not abort on some errors (like duplicate key) but instead tries to resolve them by modifying the `.ISD' file. Normally the use of two --quick options is useful only if you have too little free disk space to perform a normal repair. In this case you should at least make a backup before running isamchk.

Sommaire:

• 13.4.1 Comment vérifier une table
• 13.4.2 Comment réparer une table
• 13.4.3 Optimisation de tables