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MySQL Reference Manual :: 5.8.3.6 myisamchk Memory Usage
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- 5.8.3 Table Maintenance and Crash Recovery
- 5.8.3.1 myisamchk Invocation Syntax
- 5.8.3.2 General Options for myisamchk
- 5.8.3.3 Check Options for myisamchk
- 5.8.3.4 Repair Options for myisamchk
- 5.8.3.5 Other Options for myisamchk
- 5.8.3.6 myisamchk Memory Usage
- 5.8.3.7 Using myisamchk for Crash Recovery
- 5.8.3.8 How to Check MyISAM Tables for Errors
- 5.8.3.9 How to Repair Tables
- 5.8.3.10 Table Optimization
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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 also needs 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!
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When using
--recoveror--sort-recover(but not when using--safe-recover), you need space for a sort buffer. The amount of space required is:(
largest_key+row_pointer_length) *number_of_rows* 2You can check the length of the keys and the
row_pointer_lengthwith myisamchk -dvtbl_name. This space is allocated in the temporary directory (specified byTMPDIRor--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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