Memory allocation is important when you run myisamchk. myisamchk uses no more memory than its memory-related variables are set to. 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 512MB RAM available, you could use options such as these (in addition to any other options you might specify):
shell>myisamchk --sort_buffer_size=256M \--key_buffer_size=512M \--read_buffer_size=64M \--write_buffer_size=64M ...
Using --sort_buffer_size=16M is probably enough
for most cases.
Be aware that myisamchk uses temporary files
in TMPDIR. If TMPDIR
points to a memory file system, out of memory errors can easily
occur. If this happens, run myisamchk with
the
--tmpdir=
option to specify a directory located on a file system that has
more space.
path
When performing repair operations, myisamchk also needs a lot of disk space:
Twice the size of the data file (the original file 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 must be available on the same file system as the original data file, as 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 must be available on the same file system as the original data file.
When using
--recoveror--sort-recover(but not when using--safe-recover), you need space on disk for sorting. This space is allocated in the temporary directory (specified byTMPDIRor--tmpdir=). The following formula yields the amount of space required:path(
largest_key+row_pointer_length) *number_of_rows* 2You can check the length of the keys and the
row_pointer_lengthwith myisamchk -dvtbl_name(see Section 4.6.3.5, “Obtaining Table Information with myisamchk”). Therow_pointer_lengthandnumber_of_rowsvalues are theDatafile pointerandData recordsvalues in the table description. To determine thelargest_keyvalue, check theKeylines in the table description. TheLencolumn indicates the number of bytes for each key part. For a multiple-column index, the key size is the sum of theLenvalues for all key parts.
If you have a problem with disk space during repair, you can try
--safe-recover instead of
--recover.