MYISAMCHK(1)                 MySQL Database System                MYISAMCHK(1)

       myisamchk - MyISAM table-maintenance utility
       isamchk - ISAM table-maintenance utility

       myisamchk [options] tbl_name ...

       isamchk [options] tbl_name ...

       The myisamchk utility gets information about your database tables or
       checks, repairs, or optimizes them.  myisamchk works with MyISAM tables
       (tables that have .MYD and .MYI files for storing data and indexes). A
       related utility, isamchk, works with ISAM tables (tables that have .ISD
       and .ISM files for storing data and indexes).

       Invoke myisamchk like this:

          shell> myisamchk [options] tbl_name ...

       The options specify what you want myisamchk to do. They are described
       in the following sections. You can also get a list of options by
       invoking myisamchk --help.

       With no options, myisamchk simply checks your table as the default
       operation. To get more information or to tell myisamchk to take
       corrective action, specify options as described in the following

       tbl_name is the database table you want to check or repair. If you run
       myisamchk somewhere other than in the database directory, you must
       specify the path to the database directory, because myisamchk has no
       idea where the database is located. In fact, myisamchk does not
       actually care whether the files you are working on are located in a
       database directory. You can copy the files that correspond to a
       database table into some other location and perform recovery operations
       on them there.

       You can name several tables on the myisamchk command line if you wish.
       You can also specify a table by naming its index file (the file with
       the .MYI suffix). This allows you to specify all tables in a directory
       by using the pattern *.MYI. For example, if you are in a database
       directory, you can check all the MyISAM tables in that directory like

          shell> myisamchk *.MYI

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

          shell> myisamchk /path/to/database_dir/*.MYI

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

          shell> myisamchk /path/to/datadir/*/*.MYI

       The recommended way to quickly check all MyISAM and ISAM tables is:

          shell> myisamchk --silent --fast /path/to/datadir/*/*.MYI
          shell> isamchk --silent /path/to/datadir/*/*.ISM

       If you want to check all MyISAM and ISAM tables and repair any that are
       corrupted, you can use the following commands:

          shell> myisamchk --silent --force --fast --update-state \
                    --key_buffer_size=64M --sort_buffer_size=64M \
                    --read_buffer_size=1M --write_buffer_size=1M \
          shell> isamchk --silent --force --key_buffer_size=64M \
                    --sort_buffer_size=64M --read_buffer_size=1M --write_buffer_size=1M \

       These commands assume that you have more than 64MB free. For more
       information about memory allocation with myisamchk, see the section

       You must ensure that no other program is using the tables while you are
       running myisamchk. Otherwise, when you run myisamchk, it may display
       the following error message:

          warning: clients are using or haven't closed the table properly

       This means that you are trying to check a table that has been updated
       by another program (such as the mysqld server) that hasn't yet closed
       the file or that has died without closing the file properly.

       If mysqld is running, you must force it to flush any table
       modifications that are still buffered in memory by using FLUSH TABLES.
       You should then ensure that no one is using the tables while you are
       running myisamchk. The easiest way to avoid this problem is to use
       CHECK TABLE instead of myisamchk to check tables.

       The options described in this section can be used for any type of table
       maintenance operation performed by myisamchk. The sections following
       this one describe options that pertain only to specific operations,
       such as table checking or repairing.

       o  --help, -?

          Display a help message and exit.

       o  --debug=debug_options, -# debug_options

          Write a debugging log. The debug_options string often is

       o  --silent, -s

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

       o  --verbose, -v

          Verbose mode. Print more information about what the program does.
          This can be used with -d and -e. Use -v multiple times (-vv, -vvv)
          for even more output.

       o  --version, -V

          Display version information and exit.

       o  --wait, -w

          Instead of terminating with an error if the table is locked, wait
          until the table is unlocked before continuing. Note that if you are
          running mysqld with external locking disabled, the table can be
          locked only by another myisamchk command.

       You can also set the following variables by using --var_name=value

       |Variable          | Default Value     |
       |sort_key_blocks   | 16                |
       |stats_method      | nulls_unequal     |
       |write_buffer_size | 262136            |
       |decode_bits       | 9                 |
       |ft_max_word_len   | version-dependent |
       |ft_min_word_len   | 4                 |
       |ft_stopword_file  | built-in list     |
       |key_buffer_size   | 523264            |
       |myisam_block_size | 1024              |
       |read_buffer_size  | 262136            |
       |sort_buffer_size  | 2097144           |

       It is also possible to set variables by using
       --set-variable=var_name=value or -O var_name=value syntax. However,
       this syntax is deprecated as of MySQL 4.0.

       The possible myisamchk variables and their default values can be
       examined with myisamchk --help:

       sort_buffer_size is used when the keys are repaired by sorting keys,
       which is the normal case when you use --recover.

       key_buffer_size is used when you are checking the table with
       --extend-check or when the keys are repaired by inserting keys row by
       row into the table (like when doing normal inserts). Repairing through
       the key buffer is used in the following cases:

       o  You use --safe-recover.

       o  The temporary files needed to sort the keys would be more than twice
          as big as when creating the key file directly. This is often the
          case when you have large key values for CHAR, VARCHAR, or TEXT
          columns, because the sort operation needs to store the complete key
          values as it proceeds. If you have lots of temporary space and you
          can force myisamchk to repair by sorting, you can use the
          --sort-recover option.

       Repairing through the key buffer takes much less disk space than using
       sorting, but is also much slower.

       If you want a faster repair, set the key_buffer_size and
       sort_buffer_size variables to about 25% of your available memory. You
       can set both variables to large values, because only one of them is
       used at a time.

       myisam_block_size is the size used for index blocks. It is available as
       of MySQL 4.0.0.

       stats_method influences how NULL values are treated for index
       statistics collection when the --analyze option is given. It acts like
       the myisam_stats_method system variable. For more information, see the
       description of myisam_stats_method in the section called "SYSTEM
       VARIABLES", and Section 4.7, "MyISAM Index Statistics Collection".
       stats_method was added in MySQL 4.1.15/5.0.14. For older versions, the
       statistics collection method is equivalent to nulls_equal.

       The ft_min_word_len and ft_max_word_len variables are available as of
       MySQL 4.0.0.  ft_stopword_file is available as of MySQL 4.0.19.

       ft_min_word_len and ft_max_word_len indicate the minimum and maximum
       word length for FULLTEXT indexes.  ft_stopword_file names the stopword
       file. These need to be set under the following circumstances.

       If you use myisamchk to perform an operation that modifies table
       indexes (such as repair or analyze), the FULLTEXT indexes are rebuilt
       using the default full-text parameter values for minimum and maximum
       word length and the stopword file unless you specify otherwise. This
       can result in queries failing.

       The problem occurs because these parameters are known only by the
       server. They are not stored in MyISAM index files. To avoid the problem
       if you have modified the minimum or maximum word length or the stopword
       file in the server, specify the same ft_min_word_len, ft_max_word_len,
       and ft_stopword_file values to myisamchk that you use for mysqld. For
       example, if you have set the minimum word length to 3, you can repair a
       table with myisamchk like this:

          shell> myisamchk --recover --ft_min_word_len=3 tbl_name.MYI

       To ensure that myisamchk and the server use the same values for
       full-text parameters, you can place each one in both the [mysqld] and
       [myisamchk] sections of an option file:


       An alternative to using myisamchk is to use the REPAIR TABLE, ANALYZE
       TABLE, OPTIMIZE TABLE, or ALTER TABLE. These statements are performed
       by the server, which knows the proper full-text parameter values to

       myisamchk supports the following options for table checking operations:

       o  --check, -c

          Check the table for errors. This is the default operation if you
          specify no option that selects an operation type explicitly.

       o  --check-only-changed, -C

          Check only tables that have changed since the last check.

       o  --extend-check, -e

          Check the table very thoroughly. This is quite slow if the table has
          many indexes. This option should only be used in extreme cases.
          Normally, myisamchk or myisamchk --medium-check should be able to
          determine whether there are any errors in the table.

          If you are using --extend-check and have plenty of memory, setting
          the key_buffer_size variable to a large value helps the repair
          operation run faster.

       o  --fast, -F

          Check only tables that haven't been closed properly.

       o  --force, -f

          Do a repair operation automatically if myisamchk finds any errors in
          the table. The repair type is the same as that specified with the
          --recover or -r option.

       o  --information, -i

          Print informational statistics about the table that is checked.

       o  --medium-check, -m

          Do a check that is faster than an --extend-check operation. This
          finds only 99.99% of all errors, which should be good enough in most

       o  --read-only, -T

          Don't mark the table as checked. This is useful if you use myisamchk
          to check a table that is in use by some other application that does
          not use locking, such as mysqld when run with external locking

       o  --update-state, -U

          Store information in the .MYI file to indicate when the table was
          checked and whether the table crashed. This should be used to get
          full benefit of the --check-only-changed option, but you shouldn't
          use this option if the mysqld server is using the table and you are
          running it with external locking disabled.

       myisamchk supports the following options for table repair operations:

       o  --backup, -B

          Make a backup of the .MYD file as file_name-time.BAK

       o  --character-sets-dir=path

          The directory where character sets are installed. See Section 9.1,
          "The Character Set Used for Data and Sorting".

       o  --correct-checksum

          Correct the checksum information for the table.

       o  --data-file-length=len, -D len

          Maximum length of the data file (when re-creating data file when it
          is "full").

       o  --extend-check, -e

          Do a repair that tries to recover every possible row from the data
          file. Normally, this also finds a lot of garbage rows. Don't use
          this option unless you are totally desperate.

       o  --force, -f

          Overwrite old intermediate files (files with names like
          tbl_name.TMD) instead of aborting.

       o  --keys-used=val, -k val

          For myisamchk, the option value is a bit-value that indicates which
          indexes to update. Each binary bit of the option value corresponds
          to a table index, where the first index is bit 0. For isamchk, the
          option value indicates that only the first val of the table indexes
          should be updated. In either case, an option value of 0 disables
          updates to all indexes, which can be used to get faster inserts.
          Deactivated indexes can be reactivated by using myisamchk -r or
          (isamchk -r).

       o  --no-symlinks, -l

          Do not follow symbolic links. Normally myisamchk repairs the table
          that a symlink points to. This option does not exist as of MySQL 4.0
          because versions from 4.0 on do not remove symlinks during repair

       o  --max-record-length=len

          Skip rows larger than the given length if myisamchk cannot allocate
          memory to hold them. This option was added in MySQL 4.1.1.

       o  --parallel-recover, -p

          Uses the same technique as -r and -n, but creates all the keys in
          parallel, using different threads. This option was added in MySQL
          4.0.2.  This is beta-quality code; use at your own risk!.

       o  --quick, -q

          Achieve a faster repair by not modifying the data file. You can
          specify this option twice to force myisamchk to modify the original
          data file in case of duplicate keys.

       o  --recover, -r

          Do a repair that can fix almost any problem except unique keys that
          are not unique (which is an extremely unlikely error with
          ISAM/MyISAM tables). If you want to recover a table, this is the
          option to try first. You should try --safe-recover only if myisamchk
          reports that the table cannot be recovered by --recover. (In the
          unlikely case that --recover fails, the data file remains intact.)

          If you have lots of memory, you should increase the value of

       o  --safe-recover, -o

          Do a repair using an old recovery method that reads through all rows
          in order and updates all index trees based on the rows found. This
          is an order of magnitude slower than --recover, but can handle a
          couple of very unlikely cases that --recover cannot. This recovery
          method also uses much less disk space than --recover. Normally, you
          should repair first using --recover, and then with --safe-recover
          only if --recover fails.

          If you have lots of memory, you should increase the value of

       o  --set-character-set=name

          Change the character set used by the table indexes. This option was
          replaced by --set-collation in MySQL 4.1.1.

       o  --set-collation=name

          Specify the collation to use for sorting table indexes. The
          character set name is implied by the first part of the collation
          name. This option was added in MySQL 4.1.11.

       o  --sort-recover, -n

          Force myisamchk to use sorting to resolve the keys even if the
          temporary files should be very big.

       o  --tmpdir=path, -t path

          Path of the directory to be used for storing temporary files. If
          this is not set, myisamchk uses the value of the TMPDIR environment
          variable. Starting from MySQL 4.1, tmpdir can be set to a list of
          directory paths that are used successively in round-robin fashion
          for creating temporary files. The separator character between
          directory names should be colon (':') on Unix and semicolon (';') on
          Windows, NetWare, and OS/2.

       o  --unpack, -u

          Unpack a table that was packed with myisampack.

       myisamchk supports the following options for actions other than table
       checks and repairs:

       o  --analyze, -a

          Analyze the distribution of key values. This improves join
          performance by enabling the join optimizer to better choose the
          order in which to join the tables and which indexes it should use.
          To obtain information about the key distribution, use a myisamchk
          --description --verbose tbl_name command or the SHOW INDEX FROM
          tbl_name statement.

       o  --block-search=offset, -b offset

          Find the record that a block at the given offset belongs to.

       o  --description, -d

          Print some descriptive information about the table.

       o  --set-auto-increment[=value], -A[value]

          Force AUTO_INCREMENT numbering for new records to start at the given
          value (or higher, if there are existing records with AUTO_INCREMENT
          values this large). If value is not specified, AUTO_INCREMENT
          numbers for new records begin with the largest value currently in
          the table, plus one.

       o  --sort-index, -S

          Sort the index tree blocks in high-low order. This optimizes seeks
          and makes table scans that use indexes faster.

       o  --sort-records=N, -R N

          Sort records according to a particular index. This makes your data
          much more localized and may speed up range-based SELECT and ORDER BY
          operations that use this index. (The first time you use this option
          to sort a table, it may be very slow.) To determine a table's index
          numbers, use SHOW INDEX, which displays a table's indexes in the
          same order that myisamchk sees them. Indexes are numbered beginning
          with 1.

          If keys are not packed (PACK_KEYS=0)), they have the same length, so
          when myisamchk sorts and moves records, it just overwrites record
          offsets in the index. If keys are packed (PACK_KEYS=1), myisamchk
          must unpack key blocks first, then re-create indexes and pack the
          key blocks again. (In this case, re-creating indexes is faster than
          updating offsets for each index.)

       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 32MB RAM, you
       could use options such as these (in addition to any other options you
       might specify):

          shell> myisamchk --sort_buffer_size=16M --key_buffer_size=16M \
                     --read_buffer_size=1M --write_buffer_size=1M ...

       Using --sort_buffer_size=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, run myisamchk with the --tmpdir=path option to specify
       some directory located on a filesystem that has more space.

       When repairing, myisamchk also needs a lot of disk space:

       o  Double 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 filesystem as the original data file, as the
          copy is created in the same directory as the original.

       o  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
          filesystem as the original data file.

       o  When using --recover or --sort-recover (but not when using
          --safe-recover), you need space for a sort buffer. The following
          formula yields the amount of space required:

          (largest_key + row_pointer_length) x number_of_rows x 2
       You can check the length of the keys and the row_pointer_length with
       myisamchk -dv tbl_name. This space is allocated in the temporary
       directory (specified by TMPDIR or --tmpdir=path).

       If you have a problem with disk space during repair, you can try
       --safe-recover instead of --recover.

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MySQL 4.1                         11/02/2006                      MYISAMCHK(1)