13.1.1 Syntaxe isamchk

isamchk is invoked like this:

shell> isamchk [options] nom_table

The options specify what you want isamchk to do. They are described below. (You can also get a list of options by invoking isamchk --help.) With no options, isamchk simply checks your table. To get more information or to tell isamchk to take corrective action, specify options as described below and in the following sections.

nom_table is the database table you want to check. If you run isamchk somewhere other than in the database directory, you must specify the path to the file, since isamchk has no idea where your database is located. Actually, isamchk doesn't care whether or not the files you are working on are located in a database directory; you can copy the files that correspond to a database table into another location and perform recovery operations on them there.

You can name several tables on the isamchk command line if you wish. You can also specify a name as an index file name (with the `.ISM' suffix), which allows you to specify all tables in a directory by using the pattern `*.ISM'. For example, if you are in a database directory, you can check all the tables in the directory like this:

shell> isamchk *.ISM

If you are not in the database directory, you can check all the tables there by specifying the path to the directory:

shell> isamchk /path/to/database_dir/*.ISM

You can even check all tables in all databases by specifying a wildcard with the path to the MySQL data directory:

shell> isamchk /path/to/datadir/*/*.ISM

isamchk supports the following options:

-a, --analyze

Analyze the distribution of keys. This improves join performance by enabling the join optimizer to better choose in which order it should join the tables and which keys it should how use.

-#, --debug=debug_options

Output debug log. The debug_options string often is 'd:t:o,filename'.

-d, --description

Prints some information about the table.

-e, --extend-check

Check the table VERY thoroughly. This is necessary only in extreme cases. Normally, isamchk should find all errors even without this option.

-f, --force

Overwrite old temporary files. If you use -f when checking tables (running isamchk without -r), isamchk will automatically restart with -r on any table for which an error occurs during checking.

--help

Display a help message and exit.

-i, --information

Print informational statistics about the table that is checked.

-k #, --keys-used=#

Used with -r. Tell the NISAM table handler to update only the first # indexes. Higher-numbered indexes are deactivated. This can be used to get faster inserts! Deactivated indexes can be reactivated by using isamchk -r.

-l, --no-symlinks

Do not follow symbolic links when repairing. Normally isamchk repairs the table a symlink points at.

-q, --quick

Used with -r to get a faster repair. Normally, the original data file isn't touched; you can specify a second -q to force the original data file to be used.

-r, --recover

Recovery mode. Can fix almost anything except unique keys that aren't unique.

-o, --safe-recover

Recovery mode. Uses an old recovery méthode; this is slower than -r, but can handle a couple of cases that -r cannot handle.

-O var=option, --set-variable var=option

Set the value of a variable. The possible variables are listed below.

-s, --silent

Silent mode. Write output only when errors occur. You can use -s twice (-ss) to make isamchk very silent.

-S, --sort-index

Sort the index tree blocks in high-low order. This will optimize seeks and will make table scanning by key faster.

-R index_num, --sort-records=index_num

Sorts records according to an index. This makes your data much more localized and may speed up ranged SELECT and ORDER BY operations on this index. (It may be VERY slow to do a sort the first time!) To find out a table's index numbers, use SHOW INDEX, which shows a table's indexes in the same order that isamchk sees them. Indexes are numbered beginning with 1.

-u, --unpack

Unpack a table that was packed with pack_isam.

-v, --verbose

Verbose mode. Print more information. This can be used with -d and -e. Use -v multiple times (-vv, -vvv) for more verbosity!

-V, --version

Print the isamchk version and exit.

-w, --wait

Wait if the table is locked.

Possible variables for the --set-variable (-O) option are:

key_buffer_size       current value: 16776192
read_buffer_size      current value: 262136
write_buffer_size     current value: 262136
sort_buffer_size      current value: 2097144
sort_key_blocks       current value: 16
decode_bits           current value: 9