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 5.7.3.6 `myisamchk' Memory Usage
 ................................
 
 Memory allocation is important when you run `myisamchk'.  `myisamchk'
 uses no more memory than you specify with the `-O' options.  If you are
 going to use `myisamchk' on very large tables, you should first decide
 how much memory you want it to use.  The default is to use only about
 3MB to perform repairs.  By using larger values, you can get
 `myisamchk' to operate faster.  For example, if you have more than 32MB
 RAM, you could use options such as these (in addition to any other
 options you might specify):
 
      shell> myisamchk -O sort=16M -O key=16M -O read=1M -O write=1M ...
 
 Using `-O sort=16M' should probably be enough for most cases.
 
 Be aware that `myisamchk' uses temporary files in `TMPDIR'. If `TMPDIR'
 points to a memory filesystem, you may easily get out of memory errors.
 If this happens, set `TMPDIR' to point at some directory located on a
 filesystem with more space and run `myisamchk' again.
 
 When repairing, `myisamchk' will also need a lot of disk space:
 
    * Double the size of the data file (the original one and a copy).
      This space is not needed if you do a repair with `--quick'; in this
      case, only the index file is re-created.  This space is needed on
      the same filesystem as the original data file! (The copy is
      created in the same directory as the original.)
 
    * Space for the new index file that replaces the old one. The old
      index file is truncated at the start of the repair operation, so
      you usually ignore this space.  This space is needed on the same
      filesystem as the original index file!
 
    * When using `--recover' or `--sort-recover' (but not when using
      `--safe-recover'), you will need space for a sort buffer. The
      amount of space required is:
 
           (LARGEST_KEY + ROW_POINTER_LENGTH) * NUMBER_OF_ROWS * 2
 
      You can check the length of the keys and the `row_pointer_length'
      with `myisamchk -dv TBL_NAME'.  This space is allocated in the
      temporary directory (specified by `TMPDIR' or `--tmpdir=PATH').
 
 
 If you have a problem with disk space during repair, you can try to use
 `--safe-recover' instead of `--recover'.

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