myisamchk(1) — Linux manual page


MYISAMCHK(1)             MariaDB Database System            MYISAMCHK(1)

NAME         top

       myisamchk - MyISAM table-maintenance utility

SYNOPSIS         top

       myisamchk [options] tbl_name ...

DESCRIPTION         top

       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).

       The use of myisamchk with partitioned tables is not supported.

           It is best to make a backup of a table before performing a
           table repair operation; under some circumstances the
           operation might cause data loss. Possible causes include but
           are not limited to file system errors.

       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 MariaDB data directory:

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

       The recommended way to quickly check all MyISAM tables is:

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

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

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

       This command assumes that you have more than 64MB free. For more
       information about memory allocation with myisamchk, see the
       section called “MYISAMCHK MEMORY USAGE”.

           You must ensure that no other program is using the tables
           while you are running myisamchk. The most effective means of
           doing so is to shut down the MariaDB server while running
           myisamchk, or to lock all tables that myisamchk is being used

           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, which can sometimes lead to the corruption
           of one or more MyISAM tables.

           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

           However, the easiest way to avoid this problem is to use
           CHECK TABLE instead of myisamchk to check tables.

       myisamchk supports the following options, which can be specified
       on the command line or in the [myisamchk] option file group.


       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. Options are grouped by type
           of operation.

       •   --HELP, -H

           Display a help message and exit. Options are presented in a
           single list.

       •   --debug=debug_options, -# debug_options

           Write a debugging log. A typical debug_options string is
           ´d:t:o,file_name´. The default is

       •   --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 about what the program
           does. 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. If you
           are running mysqld with external locking disabled, the table
           can be locked only by another myisamchk command.

       •   --print-defaults

           Print the program argument list and exit.

       •   --no-defaults

           Don't read default options from any option file.

       •   --defaults-file=#

           Only read default options from the given file.

       •   --defaults-extra-file=#

           Read this file after the global files are read.

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

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

       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.

       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
       Section 5.1.4, “Server System Variables”, and Section 7.4.7,
       “MyISAM Index Statistics Collection”.

       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

       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,
       are performed by the server, which knows the proper full-text
       parameter values to use.


       myisamchk supports the following options for table checking

       •   --check, -c

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

       •   --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.

           For a description of the output format, see the section

       •   --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 --recover or -r option. States will be
           updated as with --update-state.

       •   --information, -i

           Print informational statistics about the table that is

       •   --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 external locking disabled.

       •   --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


       myisamchk supports the following options for table repair
       operations (operations performed when an option such as --recover
       or --safe-recover is given):

       •   --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.

       •   --correct-checksum

           Correct the checksum information for the table.

       •   --create-missing-keys

           Create missing keys. This assumes that the data file is
           correct and that the number of rows stored in the index file
           is correct. Enables --quick.

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

           The 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 desperate.

           For a description of the output format, see the section

       •   --force, -f

           Overwrite old intermediate files (files with names like
           tbl_name.TMD) instead of aborting. Add another --force to
           avoid 'myisam_sort_buffer_size is too small' errors. In this
           case we will attempt to do the repair with the given
           myisam_sort_buffer_size and dynamically allocate as many
           management buffers as needed.

       •   --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.
           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.

       •   --max-record-length=len

           Skip rows larger than the given length if myisamchk cannot
           allocate memory to hold them.

       •   --parallel-recover, -p

           Use the same technique as -r and -n, but create all the keys
           in parallel, using different threads.  This is beta-quality
           code. Use at your own risk!--quick, -q

           Achieve a faster repair by modifying only the index file, not
           the data file. You can specify this option twice to force
           myisamchk to modify the original data file in case of
           duplicate keys. NOTE: Tables where the data file is corrupted
           can't be fixed with this option.

       •   --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 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 using --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

       •   --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

       •   --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.

       •   --sort-recover, -n

           Force myisamchk to use sorting to resolve the keys even if
           the temporary files would be very large.

       •   --tmpdir=path, -t path

           The 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.  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 is the colon (“:”) on Unix and the
           semicolon (“;”) on Windows, NetWare, and OS/2.

       •   --unpack, -u

           Unpack a table that was packed with myisampack.


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

       •   --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.

       •   --block-search=offset, -b offset

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

       •   --description, -d

           Print some descriptive information about the table.
           Specifying the --verbose option once or twice produces
           additional information. See the section called “MYISAMCHK

       •   --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.

       •   --sort-index, -S

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

       •   --stats-method=name

           Specifies how index statistics collection code should treat
           NULLs. Possible values of name are "nulls_unequal" (default),
           "nulls_equal" (emulate MySQL 4 behavior), and


       To obtain a description of a MyISAM table or statistics about it,
       use the commands shown here. The output from these commands is
       explained later in this section.

       •   myisamchk -d tbl_name

           Runs myisamchk in “describe mode” to produce a description of
           your table. If you start the MariaDB server with external
           locking disabled, myisamchk may report an error for a table
           that is updated while it runs. However, because myisamchk
           does not change the table in describe mode, there is no risk
           of destroying data.

       •   myisamchk -dv tbl_name

           Adding -v runs myisamchk in verbose mode so that it produces
           more information about the table. Adding -v a second time
           produces even more information.

       •   myisamchk -eis tbl_name

           Shows only the most important information from a table. This
           operation is slow because it must read the entire table.

       •   myisamchk -eiv tbl_name

           This is like -eis, but tells you what is being done.

       The tbl_name argument can be either the name of a MyISAM table or
       the name of its index file, as described in myisamchk(1).
       Multiple tbl_name arguments can be given.

       Suppose that a table named person has the following structure.
       (The MAX_ROWS table option is included so that in the example
       output from myisamchk shown later, some values are smaller and
       fit the output format more easily.)

           CREATE TABLE person
             id         INT NOT NULL AUTO_INCREMENT,
             last_name  VARCHAR(20) NOT NULL,
             first_name VARCHAR(20) NOT NULL,
             birth      DATE,
             death      DATE,
             PRIMARY KEY (id),
             INDEX (last_name, first_name),
             INDEX (birth)
           ) MAX_ROWS = 1000000;

       Suppose also that the table has these data and index file sizes:

           -rw-rw----  1 mysql  mysql  9347072 Aug 19 11:47 person.MYD
           -rw-rw----  1 mysql  mysql  6066176 Aug 19 11:47 person.MYI

       Example of myisamchk -dvv output:

           MyISAM file:         person
           Record format:       Packed
           Character set:       latin1_swedish_ci (8)
           File-version:        1
           Creation time:       2009-08-19 16:47:41
           Recover time:        2009-08-19 16:47:56
           Status:              checked,analyzed,optimized keys
           Auto increment key:              1  Last value:                306688
           Data records:               306688  Deleted blocks:                 0
           Datafile parts:             306688  Deleted data:                   0
           Datafile pointer (bytes):        4  Keyfile pointer (bytes):        3
           Datafile length:           9347072  Keyfile length:           6066176
           Max datafile length:    4294967294  Max keyfile length:   17179868159
           Recordlength:                   54
           table description:
           Key Start Len Index   Type                 Rec/key         Root  Blocksize
           1   2     4   unique  long                       1        99328       1024
           2   6     20  multip. varchar prefix           512      3563520       1024
               27    20          varchar                  512
           3   48    3   multip. uint24 NULL           306688      6065152       1024
           Field Start Length Nullpos Nullbit Type
           1     1     1
           2     2     4                      no zeros
           3     6     21                     varchar
           4     27    21                     varchar
           5     48    3      1       1       no zeros
           6     51    3      1       2       no zeros

       Explanations for the types of information myisamchk produces are
       given here.  “Keyfile” refers to the index file.  “Record” and
       “row” are synonymous, as are “field” and “column.”

       The initial part of the table description contains these values:

       •   MyISAM file

           Name of the MyISAM (index) file.

       •   Record format

           The format used to store table rows. The preceding examples
           use Fixed length. Other possible values are Compressed and
           Packed. (Packed corresponds to what SHOW TABLE STATUS reports
           as Dynamic.)

       •   Chararacter set

           The table default character set.

       •   File-version

           Version of MyISAM format. Currently always 1.

       •   Creation time

           When the data file was created.

       •   Recover time

           When the index/data file was last reconstructed.

       •   Status

           Table status flags. Possible values are crashed, open,
           changed, analyzed, optimized keys, and sorted index pages.

       •   Auto increment key, Last value

           The key number associated the table´s AUTO_INCREMENT column,
           and the most recently generated value for this column. These
           fields do not appear if there is no such column.

       •   Data records

           The number of rows in the table.

       •   Deleted blocks

           How many deleted blocks still have reserved space. You can
           optimize your table to minimize this space. See
           Section 6.6.4, “MyISAM Table Optimization”.

       •   Datafile parts

           For dynamic-row format, this indicates how many data blocks
           there are. For an optimized table without fragmented rows,
           this is the same as Data records.

       •   Deleted data

           How many bytes of unreclaimed deleted data there are. You can
           optimize your table to minimize this space. See
           Section 6.6.4, “MyISAM Table Optimization”.

       •   Datafile pointer

           The size of the data file pointer, in bytes. It is usually 2,
           3, 4, or 5 bytes. Most tables manage with 2 bytes, but this
           cannot be controlled from MariaDB yet. For fixed tables, this
           is a row address. For dynamic tables, this is a byte address.

       •   Keyfile pointer

           The size of the index file pointer, in bytes. It is usually
           1, 2, or 3 bytes. Most tables manage with 2 bytes, but this
           is calculated automatically by MariaDB. It is always a block

       •   Max datafile length

           How long the table data file can become, in bytes.

       •   Max keyfile length

           How long the table index file can become, in bytes.

       •   Recordlength

           How much space each row takes, in bytes.

       The table description part of the output includes a list of all
       keys in the table. For each key, myisamchk displays some
       low-level information:

       •   Key

           This key´s number. This value is shown only for the first
           column of the key. If this value is missing, the line
           corresponds to the second or later column of a
           multiple-column key. For the table shown in the example,
           there are two table description lines for the second index.
           This indicates that it is a multiple-part index with two

       •   Start

           Where in the row this portion of the index starts.

       •   Len

           How long this portion of the index is. For packed numbers,
           this should always be the full length of the column. For
           strings, it may be shorter than the full length of the
           indexed column, because you can index a prefix of a string
           column. The total length of a multiple-part key is the sum of
           the Len values for all key parts.

       •   Index

           Whether a key value can exist multiple times in the index.
           Possible values are unique or multip.  (multiple).

       •   Type

           What data type this portion of the index has. This is a
           MyISAM data type with the possible values packed, stripped,
           or empty.

       •   Root

           Address of the root index block.

       •   Blocksize

           The size of each index block. By default this is 1024, but
           the value may be changed at compile time when MariaDB is
           built from source.

       •   Rec/key

           This is a statistical value used by the optimizer. It tells
           how many rows there are per value for this index. A unique
           index always has a value of 1. This may be updated after a
           table is loaded (or greatly changed) with myisamchk -a. If
           this is not updated at all, a default value of 30 is given.

       The last part of the output provides information about each

       •   Field

           The column number.

       •   Start

           The byte position of the column within table rows.

       •   Length

           The length of the column in bytes.

       •   Nullpos, Nullbit

           For columns that can be NULL, MyISAM stores NULL values as a
           flag in a byte. Depending on how many nullable columns there
           are, there can be one or more bytes used for this purpose.
           The Nullpos and Nullbit values, if nonempty, indicate which
           byte and bit contains that flag indicating whether the column
           is NULL.

           The position and number of bytes used to store NULL flags is
           shown in the line for field 1. This is why there are six
           Field lines for the person table even though it has only five

       •   Type

           The data type. The value may contain any of the following

           •   constant

               All rows have the same value.

           •   no endspace

               Do not store endspace.

           •   no endspace, not_always

               Do not store endspace and do not do endspace compression
               for all values.

           •   no endspace, no empty

               Do not store endspace. Do not store empty values.

           •   table-lookup

               The column was converted to an ENUM.

           •   zerofill(N)

               The most significant N bytes in the value are always 0
               and are not stored.

           •   no zeros

               Do not store zeros.

           •   always zero

               Zero values are stored using one bit.

       •   Huff tree

           The number of the Huffman tree associated with the column.

       •   Bits

           The number of bits used in the Huffman tree.

       The Huff tree and Bits fields are displayed if the table has been
       compressed with myisampack. See myisampack(1), for an example of
       this information.

       Example of myisamchk -eiv output:

           Checking MyISAM file: person
           Data records:  306688   Deleted blocks:       0
           - check file-size
           - check record delete-chain
           No recordlinks
           - check key delete-chain
           block_size 1024:
           - check index reference
           - check data record references index: 1
           Key:  1:  Keyblocks used:  98%  Packed:    0%  Max levels:  3
           - check data record references index: 2
           Key:  2:  Keyblocks used:  99%  Packed:   97%  Max levels:  3
           - check data record references index: 3
           Key:  3:  Keyblocks used:  98%  Packed:  -14%  Max levels:  3
           Total:    Keyblocks used:  98%  Packed:   89%
           - check records and index references
           *** LOTS OF ROW NUMBERS DELETED ***
           Records:            306688  M.recordlength:       25  Packed:            83%
           Recordspace used:       97% Empty space:           2% Blocks/Record:   1.00
           Record blocks:      306688  Delete blocks:         0
           Record data:       7934464  Deleted data:          0
           Lost space:         256512  Linkdata:        1156096
           User time 43.08, System time 1.68
           Maximum resident set size 0, Integral resident set size 0
           Non-physical pagefaults 0, Physical pagefaults 0, Swaps 0
           Blocks in 0 out 7, Messages in 0 out 0, Signals 0
           Voluntary context switches 0, Involuntary context switches 0
           Maximum memory usage: 1046926 bytes (1023k)

       myisamchk -eiv output includes the following information:

       •   Data records

           The number of rows in the table.

       •   Deleted blocks

           How many deleted blocks still have reserved space. You can
           optimize your table to minimize this space. See
           Section 6.6.4, “MyISAM Table Optimization”.

       •   Key

           The key number.

       •   Keyblocks used

           What percentage of the keyblocks are used. When a table has
           just been reorganized with myisamchk, the values are very
           high (very near theoretical maximum).

       •   Packed

           MariaDB tries to pack key values that have a common suffix.
           This can only be used for indexes on CHAR and VARCHAR
           columns. For long indexed strings that have similar leftmost
           parts, this can significantly reduce the space used. In the
           preceding example, the second key is 40 bytes long and a 97%
           reduction in space is achieved.

       •   Max levels

           How deep the B-tree for this key is. Large tables with long
           key values get high values.

       •   Records

           How many rows are in the table.

       •   M.recordlength

           The average row length. This is the exact row length for
           tables with fixed-length rows, because all rows have the same

       •   Packed

           MariaDB strips spaces from the end of strings. The Packed
           value indicates the percentage of savings achieved by doing

       •   Recordspace used

           What percentage of the data file is used.

       •   Empty space

           What percentage of the data file is unused.

       •   Blocks/Record

           Average number of blocks per row (that is, how many links a
           fragmented row is composed of). This is always 1.0 for
           fixed-format tables. This value should stay as close to 1.0
           as possible. If it gets too large, you can reorganize the
           table. See Section 6.6.4, “MyISAM Table Optimization”.

       •   Recordblocks

           How many blocks (links) are used. For fixed-format tables,
           this is the same as the number of rows.

       •   Deleteblocks

           How many blocks (links) are deleted.

       •   Recorddata

           How many bytes in the data file are used.

       •   Deleted data

           How many bytes in the data file are deleted (unused).

       •   Lost space

           If a row is updated to a shorter length, some space is lost.
           This is the sum of all such losses, in bytes.

       •   Linkdata

           When the dynamic table format is used, row fragments are
           linked with pointers (4 to 7 bytes each).  Linkdata is the
           sum of the amount of storage used by all such pointers.


       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

           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

       Be aware that myisamchk uses temporary files in TMPDIR. If TMPDIR
       points to a memory file system, out of memory errors can easily
       occur. If this happens, run myisamchk with the --tmpdir=path
       option to specify a directory located on a file system that has
       more space.

       When performing repair operations, myisamchk also needs a lot of
       disk space:

       •   Twice 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 file system 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 file system as the original data

       •   When using --recover or --sort-recover (but not when using
           --safe-recover), you need space on disk for sorting. This
           space is allocated in the temporary directory (specified by
           TMPDIR or --tmpdir=path). The following formula yields the
           amount of space required:

               (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 (see the
           section called “MYISAMCHK TABLE INFORMATION”). The
           row_pointer_length and number_of_rows values are the Datafile
           pointer and Data records values in the table description. To
           determine the largest_key value, check the Key lines in the
           table description. The Len column indicates the number of
           bytes for each key part. For a multiple-column index, the key
           size is the sum of the Len values for all key parts.

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

COPYRIGHT         top

       Copyright 2007-2008 MySQL AB, 2008-2010 Sun Microsystems, Inc.,
       2010-2020 MariaDB Foundation

       This documentation is free software; you can redistribute it
       and/or modify it only under the terms of the GNU General Public
       License as published by the Free Software Foundation; version 2
       of the License.

       This documentation is distributed in the hope that it will be
       useful, but WITHOUT ANY WARRANTY; without even the implied
       See the GNU General Public License for more details.

       You should have received a copy of the GNU General Public License
       along with the program; if not, write to the Free Software
       Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
       02110-1335 USA or see

SEE ALSO         top

       For more information, please refer to the MariaDB Knowledge Base,
       available online at

AUTHOR         top

       MariaDB Foundation (

COLOPHON         top

       This page is part of the MariaDB (MariaDB database server)
       project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug report for this manual
       page, see ⟨⟩.
       This page was obtained from the project's upstream Git repository
       ⟨⟩ on 2023-06-23.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2023-05-11.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

MariaDB 10.8                   15 May 2020                  MYISAMCHK(1)

Pages that refer to this page: aria_chk(1)myisamchk(1)myisampack(1)