SpirirHost Support Centre: MySQL Reference Manual p.237

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Table of Contents
1. General Information
2. MySQL Installation
3. Tutorial Introduction
4. Database Administration
5. MySQL Optimisation
6. MySQL Language Reference
7. MySQL Table Types
8. MySQL APIs
9. Extending MySQL

Chapter 4: Database Administration 237 you should rst decide how much memory you want it to use. The default is to use only about 3M to x things. By using larger values, you can get myisamchk to operate faster. For example, if you have more than 32M 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 les in TMPDIR. If TMPDIR points to a memory lesystem, you may easily get out of memory errors. If this happens, set TMPDIR to point at some directory with more space and restart myisamchk. When repairing, myisamchk will also need a lot of disk space: Double the size of the record le (the original one and a copy). This space is not needed if one does a repair with --quick, as in this case only the index le will be re-created. This space is needed on the same disk as the original record le! Space for the new index le that replaces the old one. The old index le is truncated at start, so one usually ignore this space. This space is needed on the same disk as the original index le! When using --recover or --sort-recover (but not when using --safe-recover), you will need space for a sort buer for: (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 table. This space is allocated on the temporary disk (specied by TMPDIR or --tmpdir=#). If you have a problem with disk space during repair, you can try to use --safe-recover instead of --recover. 4.4.6.7 Using myisamchk for Crash Recovery If you run mysqld with --skip-external-locking (which is the default on some systems, like Linux), you can't reliably use myisamchk to check a table when mysqld is using the same table. If you can be sure that no one is accessing the tables through mysqld while you run myisamchk, you only have to do mysqladmin flush-tables before you start checking the tables. If you can't guarantee the above, then you must take down mysqld while you check the tables. If you run myisamchk while mysqld is updating the tables, you may get a warning that a table is corrupt even if it isn't. If you are not using --skip-external-locking, you can use myisamchk to check tables at any time. While you do this, all clients that try to update the table will wait until myisamchk is ready before continuing. If you use myisamchk to repair or optimise tables, you must always ensure that the mysqld server is not using the table (this also applies if you are using --skip-external-locking). If you don't take down mysqld you should at least do a mysqladmin flush-tables before you run myisamchk. Your tables may be corrupted if the server and myisamchk access the tables simultaneously. This chapter describes how to check for and deal with data corruption in MySQL databases. If your tables get corrupted frequently you should try to nd the reason for this! See Section A.4.1 [Crashing], page 640.

MySQL Reference Manual

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