Description, check and repair of MyISAM tables.
Used without options all tables on the command will be checked for errorsUsage: myisamchk [OPTIONS] tables[.MYI]
Global options:
-H, --HELP Display this help and exit. -?, --help Display this help and exit. -O, --set-variable var=option. Change the value of a variable. Please note that this option is deprecated; you can set variables directly with '--variable-name=value'. -t, --tmpdir=path Path for temporary files. Multiple paths can be specified, separated by colon (:), they will be used in a round-robin fashion. -s, --silent Only print errors. One can use two -s to make myisamchk very silent. -v, --verbose Print more information. This can be used with --description and --check. Use many -v for more verbosity. -V, --version Print version and exit. -w, --wait Wait if table is locked.Check options (check is the default action for myisamchk):
-c, --check Check table for errors. -e, --extend-check Check the table VERY throughly. Only use this in extreme cases as myisamchk should normally be able to find out if the table is ok even without this switch. -F, --fast Check only tables that haven't been closed properly. -C, --check-only-changed Check only tables that have changed since last check. -f, --force Restart with '-r' if there are any errors in the table. States will be updated as with '--update-state'. -i, --information Print statistics information about table that is checked. -m, --medium-check Faster than extend-check, but only finds 99.99% of all errors. Should be good enough for most cases. -U --update-state Mark tables as crashed if you find any errors. -T, --read-only Don't mark table as checked.Repair options (When using '-r' or '-o'):
-B, --backup Make a backup of the .MYD file as 'filename-time.BAK'. --correct-checksum Correct checksum information for table. -D, --data-file-length=# Max length of data file (when recreating data file when it's full). -e, --extend-check Try to recover every possible row from the data file Normally this will also find a lot of garbage rows; Don't use this option if you are not totally desperate. -f, --force Overwrite old temporary files. -k, --keys-used=# Tell MyISAM to update only some specific keys. # is a bit mask of which keys to use. This can be used to get faster inserts. --max-record-length=# Skip rows bigger than this if myisamchk can't allocate memory to hold it. -r, --recover Can fix almost anything except unique keys that aren't unique. -n, --sort-recover Forces recovering with sorting even if the temporary file would be very big. -p, --parallel-recover Uses the same technique as '-r' and '-n', but creates all the keys in parallel, in different threads. -o, --safe-recover Uses old recovery method; Slower than '-r' but can handle a couple of cases where '-r' reports that it can't fix the data file. --character-sets-dir=... Directory where character sets are. --set-collation=name Change the collation used by the index. -q, --quick Faster repair by not modifying the data file. One can give a second '-q' to force myisamchk to modify the original datafile in case of duplicate keys. NOTE: Tables where the data file is currupted can't be fixed with this option. -u, --unpack Unpack file packed with myisampack.Other actions:
-a, --analyze Analyze distribution of keys. Will make some joins in MySQL faster. You can check the calculated distribution by using '--description --verbose table_name'. --stats_method=name Specifies how index statistics collection code should treat NULLs. Possible values of name are "nulls_unequal" (default for 4.1/5.0), "nulls_equal" (emulate 4.0), and "nulls_ignored". -d, --description Prints some information about table. -A, --set-auto-increment[=value] Force auto_increment to start at this or higher value If no value is given, then sets the next auto_increment value to the highest used value for the auto key + 1. -S, --sort-index Sort index blocks. This speeds up 'read-next' in applications. -R, --sort-records=# Sort records according to an index. This makes your data much more localized and may speed up things (It may be VERY slow to do a sort the first time!). -b, --block-search=# Find a record, a block at given offset belongs to.
由于临时断电，使用kill -9中止MySQL服务进程，所有的这些都可能会毁坏MySQL的数据文件。如果在被干扰时，服务正在改变文件，文件可能会留下错误的或不一致的状态。因为这样的毁坏有时是不容易被发现的，当你发现这个错误时可能是很久以后的事了。于是，当你发现这个问题时，也许所有的备份都有同样的错误。
myisamchk通过一行一行地创建一个“.MYD”(数据 )文件的副本来工作，它通过由删除老的“.MYD 文件并且重命名新文件到原来的文件名结束修复阶段。如果你使用--quick，myisamchk不创建一个临时“.MYD”文件，只是假定“.MYD”文件是正确的并且仅创建一个新的索引文件，不接触“.MYD”文件，这是安全的，因为myisamchk自动检测“.MYD”文件是否损坏并且在这种情况下，放弃修复。你也可以给myisamchk两个--quick选项。在这种情况下，myisamchk不会在一些错误上(象重复键)放弃，相反试图通过修改“.MYD”文件解决它们。通常，只有在你在太少的空闲磁盘空间上实施一个正常修复，使用两个--quick选项才有用。在这种情况下，你应该至少在运行myisamchk前做一个备份。
1、myisamchk
使用myisamchk必须暂时停止MySQL服务器。例如，我们要检修test数据库。执行以下操作：# service mysqld stop ;# myisamchk -r /var/lib/mysql/test/*MYI# service mysqld start;
myisamchk会自动检查并修复数据表中的索引错误。
2、mysqlcheck
使用mysqlcheck无需停止MySQL，可以进行热修复。#mysqlcheck –r DBname Tablename –uuser –ppassword
注意，无论是myisamchk还是mysqlcheck，一般情况下不要使用-f强制修复，-f参数会在遇到一般修复无法成功的时候删除