myisamchk

• When performing crash recovery, it is important to understand that each MyISAM 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.
  • Problems occur most often in data files and index files.

    File	Purpose
    tbl_name.frm	Definition (format) file
    tbl_name.MYD	Data file
    tbl_name.MYI	Index file

• 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.
  • If the --quick option is used, the temporary file is not created.
    • It assumes that the .MYD file is correct and generates only a new index file without touching the .MYD file.
    • This is safe, because myisamchk automatically detects whether the .MYD file is corrupt and aborts the repair if it is corrupt.
  • The -e option does a complete and thorough check of all data.
    • -e means extended check.

What are symptoms of corrupted tables?

---

---

© 2007 John Michael Pierobon

Notes