myisamchk



MYISAMCHK(1)                 MySQL Database System                MYISAMCHK(1)




NAME

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


SYNOPSIS

       myisamchk [options] tbl_name ...

       isamchk [options] tbl_name ...


DESCRIPTION

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

       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
       discussion.

       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
       this:

       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 \
                 -O key_buffer=64M -O sort_buffer=64M \
                 -O read_buffer=1M -O write_buffer=1M \
                 /path/to/datadir/*/*.MYI
       shell> isamchk --silent --force -O key_buffer=64M \
                 -O sort_buffer=64M -O read_buffer=1M -O write_buffer=1M \
                 /path/to/datadir/*/*.ISM

       These commands assume that you have more than 64MB free. For more
       information about memory allocation with myisamchk, see the section
       called “\FBMYISAMCHK\FR MEMORY USAGE”.

       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.


GENERAL OPTIONS FOR MYISAMCHK

       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.

       ·  --help, -?

          Display a help message and exit.

       ·  --debug=debug_options, -# debug_options

          Write a debugging log. The debug_options string often is
          ´d:t:o,file_name’.

       ·  --silent, -s

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

       ·  --verbose, -v

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

       ·  --version, -V

          Display version information and exit.

       ·  --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 the --skip-external-locking option, the table
          can be locked only by another myisamchk command.

       You can also set the following variables by using --var_name=value
       options: VariableDefault
       Valuedecode_bits9ft_max_word_lenversion-dependentft_min_word_len4ft_stopword_filebuilt-in
       listkey_buffer_size523264myisam_block_size1024read_buffer_size262136sort_buffer_size2097144sort_key_blocks16stats_methodnulls_unequalwrite_buffer_size262136.PP
       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:

       ·  You use --safe-recover.

       ·  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 “SERVER 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:

       [mysqld]
       ft_min_word_len=3
       [myisamchk]
       ft_min_word_len=3

       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
       use.


CHECK OPTIONS FOR MYISAMCHK

       myisamchk supports the following options for table checking operations:

       ·  --check, -c

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

       ·  --check-only-changed, -C

          Check only tables that have changed since the last check.

       ·  --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.

       ·  --fast, -F

          Check only tables that haven’t been closed properly.

       ·  --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
          --repair or -r option.

       ·  --information, -i

          Print informational statistics about the table that is checked.

       ·  --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
          cases.

       ·  --read-only, -T

          do not 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 the
          --skip-external-locking option.

       ·  --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 should not
          use this option if the mysqld server is using the table and you are
          running it with the --skip-external-locking option.


REPAIR OPTIONS FOR MYISAMCHK

       myisamchk supports the following options for table repair operations:

       ·  --backup, -B

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

       ·  --character-sets-dir=path

          The directory where character sets are installed. See Section 7.1,
          “The Character Set Used for Data and Sorting”.

       ·  --correct-checksum

          Correct the checksum information for the table.

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

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

       ·  --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. do not use
          this option unless you are totally desperate.

       ·  --force, -f

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

       ·  --keys-used=val, -k val

          For myisamchk, the option value is a bit-value 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).

       ·  --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 operations.

       ·  --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 alpha code; use at your own risk.

       ·  --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.

       ·  --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 -o only if myisamchk reports
          that the table cannot be recovered by -r. (In the unlikely case that
          -r fails, the data file remains intact.)

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

       ·  --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 -r, but can handle a couple of
          very unlikely cases that -r cannot. This recovery method also uses
          much less disk space than -r. Normally, you should repair first
          using -r, and then with -o only if -r fails.

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

       ·  --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.

       ·  --set-collation=name

          Change the collation used to sort 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.

       ·  --sort-recover, -n

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

       ·  --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.

       ·  --unpack, -u

          Unpack a table that was packed with myisampack.


OTHER OPTIONS FOR MYISAMCHK

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

       ·  --analyze, -a

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

       ·  --description, -d

          Print some descriptive information about the table.

       ·  --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 number
          for new records begins with the largest value currently in the
          table, plus one.

       ·  --sort-index, -S

          Sort the index tree blocks in high-low order. This optimizes seeks
          and makes table scanning by key faster.

       ·  --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 KEYS, 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 recreate indexes and pack the key
          blocks again. (In this case, recreating indexes is faster than
          updating offsets for each index.)


MYISAMCHK MEMORY USAGE

       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 must be available on
          the same filesystem as the original data file, as 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 must be available on the same
          filesystem as the original data file.

       ·  When using --recover or --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 * 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 to use
       --safe-recover instead of --recover.


USING MYISAMCHK FOR CRASH RECOVERY

       If you run mysqld with --skip-external-locking (which is the default on
       some systems, such as Linux), you cannot 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 cannot guarantee this, then you must stop
       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
       when it is not.

       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 wait until myisamchk is ready before continuing.

       If you use myisamchk to repair or optimize 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 do not take down
       mysqld, you should at least do a mysqladmin flush-tables before you run
       myisamchk. Your tables may become corrupted if the server and myisamchk
       access the tables simultaneously.

       This section describes how to check for and deal with data corruption
       in MySQL databases. If your tables are corrupted frequently you should
       try to find the reason why. See Section 4.2, “What to Do If MySQL Keeps
       Crashing”.

       The MyISAM table section discusses some reasons why a table could be
       corrupted. See Section 1.4, “MyISAM Table Problems”.

       When performing crash recovery, it is important to understand that each
       MyISAM table tbl_name in a database corresponds to three files in the
       database directory: FilePurposetbl_name.frmDefinition (format)
       filetbl_name.MYDData filetbl_name.MYIIndex file.PP Each of these three
       file types is subject to corruption in various ways, but problems occur
       most often in data files and index files.

       myisamchk works by creating a copy of the .MYD data file row by row. It
       ends the repair stage by removing the old .MYD file and renaming the
       new file to the original file name. If you use --quick, myisamchk does
       not create a temporary .MYD file, but instead assumes that the .MYD
       file is correct and only generates a new index file without touching
       the .MYD file. This is safe, because myisamchk automatically detects
       whether the .MYD file is corrupt and aborts the repair if it is. You
       can also specify the --quick option twice to myisamchk. In this case,
       myisamchk does not abort on some errors (such as duplicate-key errors)
       but instead tries to resolve them by modifying the .MYD file. Normally
       the use of two --quick options is useful only if you have too little
       free disk space to perform a normal repair. In this case, you should at
       least make a backup before running myisamchk.


HOW TO CHECK MYISAM TABLES FOR ERRORS

       To check a MyISAM table, use the following commands:

       ·  myisamchk tbl_name

          This finds 99.99% of all errors. What it cannot find is corruption
          that involves only the data file (which is very unusual). If you
          want to check a table, you should normally run myisamchk without
          options or using the -s or --silent option.

       ·  myisamchk -m tbl_name

          This finds 99.999% of all errors. It first checks all index entries
          for errors and then reads through all rows. It calculates a checksum
          for all keys in the rows and verifies that the checksum matches the
          checksum for the keys in the index tree.

       ·  myisamchk -e tbl_name

          This does a complete and thorough check of all data (-e means
          “extended check”). It does a check-read of every key for each row to
          verify that they indeed point to the correct row. This may take a
          long time for a large table that has many indexes. Normally,
          myisamchk stops after the first error it finds. If you want to
          obtain more information, you can add the --verbose (-v) option. This
          causes myisamchk to continue, up to a maximum of 20 errors.

       ·  myisamchk -e -i tbl_name

          Like the previous command, but the -i option tells myisamchk to
          print additional statistical information.

       In most cases, a simple myisamchk with no arguments other than the
       table name is sufficient to check a table.


HOW TO REPAIR TABLES

       The discussion in this section describes how to use myisamchk on MyISAM
       tables (extensions .MYI and .MYD). If you are using ISAM tables
       (extensions .ISM and .ISD), you should use isamchk instead; the
       concepts are similar.

       If you are using MySQL 3.23.16 and above, you can (and should) use the
       CHECK TABLE and REPAIR TABLE statements to check and repair MyISAM
       tables. See Section 5.2.3, “CHECK TABLE Syntax” and Section 5.2.6,
       “REPAIR TABLE Syntax”.

       The symptoms of a corrupted table include queries that abort
       unexpectedly and observable errors such as these:

       ·  tbl_name.frm is locked against change

       ·  cannot find file tbl_name.MYI (Errcode: nnn)

       ·  Unexpected end of file

       ·  Record file is crashed

       ·  Got error nnn from table handler

       To get more information about the error you can run perrornnn, where
       nnn is the error number. The following example shows how to use perror
       to find the meanings for the most common error numbers that indicate a
       problem with a table:

       shell> perror 126 127 132 134 135 136 141 144 145
       126 = Index file is crashed / Wrong file format
       127 = Record-file is crashed
       132 = Old database file
       134 = Record was already deleted (or record file crashed)
       135 = No more room in record file
       136 = No more room in index file
       141 = Duplicate unique key or constraint on write or update
       144 = Table is crashed and last repair failed
       145 = Table was marked as crashed and should be repaired

       Note that error 135 (no more room in record file) and error 136 (no
       more room in index file) are not errors that can be fixed by a simple
       repair. In this case, you have to use ALTER TABLE to increase the
       MAX_ROWS and AVG_ROW_LENGTH table option values:

       ALTER TABLE tbl_name MAX_ROWS=xxx AVG_ROW_LENGTH=yyy;

       If you do not know the current table option values, use SHOW CREATE
       TABLE tbl_name.

       For the other errors, you must repair your tables.  myisamchk can
       usually detect and fix most problems that occur.

       The repair process involves up to four stages, described here. Before
       you begin, you should change location to the database directory and
       check the permissions of the table files. On Unix, make sure that they
       are readable by the user that mysqld runs as (and to you, because you
       need to access the files you are checking). If it turns out you need to
       modify files, they must also be writable by you.

       The options that you can use for table maintenance with myisamchk and
       isamchk are described in several of the earlier subsections of
       myisamchk(1).

       The following section is for the cases where the above command fails or
       if you want to use the extended features that myisamchk and isamchk
       provide.

       If you are going to repair a table from the command line, you must
       first stop the mysqld server. Note that when you do mysqladmin shutdown
       on a remote server, the mysqld server is still alive for a while after
       mysqladmin returns, until all queries are stopped and all keys have
       been flushed to disk.

       Stage 1: Checking your tables

       Run myisamchk *.MYI or myisamchk -e *.MYI if you have more time. Use
       the -s (silent) option to suppress unnecessary information.

       If the mysqld server is down, you should use the --update-state option
       to tell myisamchk to mark the table as ’checked’.

       You have to repair only those tables for which myisamchk announces an
       error. For such tables, proceed to Stage 2.

       If you get strange errors when checking (such as out of memory), or if
       myisamchk crashes, go to Stage 3.

       Stage 2: Easy safe repair

       Note: If you want a repair operation to go much faster, you should set
       the values of the sort_buffer_size and key_buffer_size variables each
       to about 25% of your available memory when running myisamchk or
       isamchk.

       First, try myisamchk -r -q tbl_name (-r -q means “quick recovery
       mode”). This attempts to repair the index file without touching the
       data file. If the data file contains everything that it should and the
       delete links point at the correct locations within the data file, this
       should work, and the table is fixed. Start repairing the next table.
       Otherwise, use the following procedure:

       1. Make a backup of the data file before continuing.

       2. Use myisamchk -r tbl_name (-r means “recovery mode”). This removes
          incorrect and deleted records from the data file and reconstructs
          the index file.

       3. If the preceding step fails, use myisamchk --safe-recover tbl_name.
          Safe recovery mode uses an old recovery method that handles a few
          cases that regular recovery mode does not (but is slower).

       If you get strange errors when checking (such as out of memory), or if
       myisamchk crashes, go to Stage 3.

       Stage 3: Difficult repair

       You should reach this stage only if the first 16KB block in the index
       file is destroyed or contains incorrect information, or if the index
       file is missing. In this case, it is necessary to create a new index
       file. Do so as follows:

       1. Move the data file to a safe place.

       2. Use the table description file to create new (empty) data and index
          files:

          shell> mysql db_name
          mysql> SET AUTOCOMMIT=1;
          mysql> TRUNCATE TABLE tbl_name;
          mysql> quit
          If your version of MySQL does not have TRUNCATE TABLE, use DELETE
          FROM tbl_name instead.

       3. Copy the old data file back onto the newly created data file. (do
          not just move the old file back onto the new file; you want to
          retain a copy in case something goes wrong.)

       Go back to Stage 2.  myisamchk -r -q should work. (This should not be
       an endless loop.)

       As of MySQL 4.0.2, you can also use REPAIR TABLE tbl_name USE_FRM,
       which performs the whole procedure automatically.

       Stage 4: Very difficult repair

       You should reach this stage only if the .frm description file has also
       crashed. That should never happen, because the description file is not
       changed after the table is created:

       1. Restore the description file from a backup and go back to Stage 3.
          You can also restore the index file and go back to Stage 2. In the
          latter case, you should start with myisamchk -r.

       2. If you do not have a backup but know exactly how the table was
          created, create a copy of the table in another database. Remove the
          new data file, then move the .frm description and .MYI index files
          from the other database to your crashed database. This gives you new
          description and index files, but leaves the .MYD data file alone. Go
          back to Stage 2 and attempt to reconstruct the index file.


TABLE OPTIMIZATION

       To coalesce fragmented records and eliminate wasted space resulting
       from deleting or updating records, run myisamchk in recovery mode:

       shell> myisamchk -r tbl_name

       You can optimize a table in the same way by using the SQL OPTIMIZE
       TABLE statement.  OPTIMIZE TABLE does a repair of the table and a key
       analysis, and also sorts the index tree to give faster key lookups.
       There is also no possibility of unwanted interaction between a utility
       and the server, because the server does all the work when you use
       OPTIMIZE TABLE. See Section 5.2.5, “OPTIMIZE TABLE Syntax”.

       myisamchk also has a number of other options you can use to improve the
       performance of a table:

       ·  -S, --sort-index

       ·  -R index_num, --sort-records=index_num

       ·  -a, --analyze

       For a full description of all available options, see myisamchk(1).


SEE ALSO

       isamchk(1), isamlog(1), msql2mysql(1), myisamlog(1), myisampack(1),
       mysql(1), mysql.server(1), mysql_config(1),
       mysql_fix_privilege_tables(1), mysql_zap(1), mysqlaccess(1),
       mysqladmin(1), mysqlbinlog(1), mysqlcheck(1), mysqld(1),
       mysqld_multi(1), mysqld_safe(1), mysqldump(1), mysqlhotcopy(1),
       mysqlimport(1), mysqlshow(1), pack_isam(1), perror(1), replace(1),
       safe_mysqld(1)

       For more information, please refer to the MySQL Reference Manual, which
       may already be installed locally and which is also available online at
       http://dev.mysql.com/doc/.


AUTHOR

       MySQL AB (http://www.mysql.com/).  This software comes with no
       warranty.



MySQL 4.1                         11/30/2005                      MYISAMCHK(1)

Man(1) output converted with man2html