4.6.3.3 myisamchk Repair Options

myisamchk supports the following options for table repair operations (operations performed when an option such as --recover or --safe-recover is given):

• --backup, -B

  Command-Line Format	--backup

  Make a backup of the .MYD file as file_name-time.BAK

• --character-sets-dir=dir_name

  Command-Line Format	--character-sets-dir=path
  Type	String
  Default Value	[none]

  The directory where character sets are installed. See Section 10.15, “Character Set Configuration”.

• --correct-checksum

  Command-Line Format	--correct-checksum

  Correct the checksum information for the table.

• --data-file-length=len, -D len

  Command-Line Format	--data-file-length=len
  Type	Numeric

  The maximum length of the data file (when re-creating data file when it is “full”).

• --extend-check, -e

  Command-Line Format	--extend-check

  Do a repair that tries to recover every possible row from the data file. Normally, this also finds a lot of garbage rows. Do not use this option unless you are desperate.

  See also the description of this option under table checking options.

  For a description of the output format, see Section 4.6.3.5, “Obtaining Table Information with myisamchk”.

• --force, -f

  Command-Line Format	--force

  Overwrite old intermediate files (files with names like tbl_name.TMD) instead of aborting.

• --keys-used=val, -k val

  Command-Line Format	--keys-used=val
  Type	Numeric

  For myisamchk, the option value is a bit value that indicates which indexes to update. Each binary bit of the option value corresponds to a table index, where the first index is bit 0. An option value of 0 disables updates to all indexes, which can be used to get faster inserts. Deactivated indexes can be reactivated by using myisamchk -r.

• --max-record-length=len

  Command-Line Format	--max-record-length=len
  Type	Numeric

  Skip rows larger than the given length if myisamchk cannot allocate memory to hold them.

• --parallel-recover, -p

  Command-Line Format	--parallel-recover

  Note

  This option is deprecated in MySQL 5.7.38 and removed in MySQL 5.7.39.

  Use the same technique as -r and -n, but create all the keys in parallel, using different threads. This is beta-quality code. Use at your own risk!

• --quick, -q

  Command-Line Format	--quick

  Achieve a faster repair by modifying only the index file, not the data file. You can specify this option twice to force myisamchk to modify the original data file in case of duplicate keys.

• --recover, -r

  Command-Line Format	--recover

  Do a repair that can fix almost any problem except unique keys that are not unique (which is an extremely unlikely error with MyISAM tables). If you want to recover a table, this is the option to try first. You should try --safe-recover only if myisamchk reports that the table cannot be recovered using --recover. (In the unlikely case that --recover fails, the data file remains intact.)

  If you have lots of memory, you should increase the value of myisam_sort_buffer_size.

• --safe-recover, -o

  Command-Line Format	--safe-recover

  Do a repair using an old recovery method that reads through all rows in order and updates all index trees based on the rows found. This is an order of magnitude slower than --recover, but can handle a couple of very unlikely cases that --recover cannot. This recovery method also uses much less disk space than --recover. Normally, you should repair first using --recover, and then with --safe-recover only if --recover fails.

  If you have lots of memory, you should increase the value of key_buffer_size.

• --set-collation=name

  Command-Line Format	--set-collation=name
  Type	String

  Specify the collation to use for sorting table indexes. The character set name is implied by the first part of the collation name.

• --sort-recover, -n

  Command-Line Format	--sort-recover

  Force myisamchk to use sorting to resolve the keys even if the temporary files would be very large.

• --tmpdir=dir_name, -t dir_name

  Command-Line Format	--tmpdir=dir_name
  Type	Directory name

  The path of the directory to be used for storing temporary files. If this is not set, myisamchk uses the value of the TMPDIR environment variable. --tmpdir can be set to a list of directory paths that are used successively in round-robin fashion for creating temporary files. The separator character between directory names is the colon (:) on Unix and the semicolon (;) on Windows.

• --unpack, -u

  Command-Line Format	--unpack

  Unpack a table that was packed with myisampack.