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myisamchk(1)                 MySQL Database System                myisamchk(1)


       myisamchk - MyISAM table-maintenance utility


       myisamchk [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).

       You can also use the CHECK TABLE and REPAIR TABLE statements to check
       and repair MyISAM tables. See Section, "CHECK TABLE Syntax",
       and Section, "REPAIR TABLE Syntax".

       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

       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 enables 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 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 --myisam_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

       For additional information about using myisamchk, see Section 7.6,
       "MyISAM Table Maintenance and Crash Recovery".

           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 MySQL server while running myisamchk, or to lock all
           tables that myisamchk is being used on.

           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. See Section,
           "CHECK TABLE Syntax".

       myisamchk supports the following options, which can be specified on the
       command line or in the [myisamchk] group of an option file. For
       information about option files used by MySQL programs, see
       Section 4.2.6, "Using Option Files".


       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. Options are grouped by type of

       o   --HELP, -H

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

       o   --debug=debug_options, -# debug_options

           Write a debugging log. A typical debug_options string is
           d:t:o,file_name. The default is d:t:o,/tmp/myisamchk.trace.

       o   --defaults-extra-file=file_name

           Read this option file after the global option file but (on Unix)
           before the user option file. If the file does not exist or is
           otherwise inaccessible, an error occurs.  file_name is interpreted
           relative to the current directory if given as a relative path name
           rather than a full path name.

           For additional information about this and other option-file
           options, see Section 4.2.7, "Command-Line Options that Affect
           Option-File Handling".

       o   --defaults-file=file_name

           Use only the given option file. If the file does not exist or is
           otherwise inaccessible, an error occurs.  file_name is interpreted
           relative to the current directory if given as a relative path name
           rather than a full path name.

           For additional information about this and other option-file
           options, see Section 4.2.7, "Command-Line Options that Affect
           Option-File Handling".

       o   --defaults-group-suffix=str

           Read not only the usual option groups, but also groups with the
           usual names and a suffix of str. For example, myisamchk normally
           reads the [myisamchk] group. If the --defaults-group-suffix=_other
           option is given, myisamchk also reads the [myisamchk_other] group.

           For additional information about this and other option-file
           options, see Section 4.2.7, "Command-Line Options that Affect
           Option-File Handling".

       o   --no-defaults

           Do not read any option files. If program startup fails due to
           reading unknown options from an option file, --no-defaults can be
           used to prevent them from being read.

           The exception is that the .mylogin.cnf file, if it exists, is read
           in all cases. This permits passwords to be specified in a safer way
           than on the command line even when --no-defaults is used.
           (.mylogin.cnf is created by the mysql_config_editor utility. See

           For additional information about this and other option-file
           options, see Section 4.2.7, "Command-Line Options that Affect
           Option-File Handling".

       o   --print-defaults

           Print the program name and all options that it gets from option

           For additional information about this and other option-file
           options, see Section 4.2.7, "Command-Line Options that Affect
           Option-File Handling".

       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. 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     |
       |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              |
       |myisam_sort_key_blocks | 16                |
       |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:

       myisam_sort_buffer_size is used when the keys are repaired by sorting
       keys, which is the normal case when you use --recover.
       sort_buffer_size is a deprecated synonym for myisam_sort_buffer_size.

       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
       myisam_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 5.1.7, "Server System
       Variables", and Section 8.3.7, "InnoDB and MyISAM Index Statistics

       ft_min_word_len and ft_max_word_len indicate the minimum and maximum
       word length for FULLTEXT indexes on MyISAM tables.  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, 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.

           See also the description of this option under table repair options.

           For a description of the output format, see the section called

       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 cases.

       o   --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.

       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
       (operations performed when an option such as --recover or
       --safe-recover is given):

       o   --backup, -B

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

       o   --character-sets-dir=dir_name

           The directory where character sets are installed. See
           Section 10.14, "Character Set Configuration".

       o   --correct-checksum

           Correct the checksum information for the table.

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

           The 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. Do not use
           this option unless you are desperate.

           See also the description of this option under table checking

           For a description of the output format, see the section called

       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. 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.

       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 operations.

       o   --max-record-length=len

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

       o   --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!

       o   --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.

       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 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

       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-collation=name

           Specify the collation to use for sorting table indexes. The
           character set name is implied by the first part of the collation

       o   --sort-recover, -n

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

       o   --tmpdir=dir_name, -t dir_name

           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.

       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. Specifying the
           --verbose option once or twice produces additional information. See

       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.)


       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.

       o   myisamchk -d tbl_name

           Runs myisamchk in "describe mode" to produce a description of your
           table. If you start the MySQL 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.

       o   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.

       o   myisamchk -eis tbl_name

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

       o   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 ENGINE=MYISAM;

       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:

       o   MyISAM file

           Name of the MyISAM (index) file.

       o   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.)

       o   Chararacter set

           The table default character set.

       o   File-version

           Version of MyISAM format. Always 1.

       o   Creation time

           When the data file was created.

       o   Recover time

           When the index/data file was last reconstructed.

       o   Status

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

       o   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.

       o   Data records

           The number of rows in the table.

       o   Deleted blocks

           How many deleted blocks still have reserved space. You can optimize
           your table to minimize this space. See Section 7.6.4, "MyISAM Table

       o   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.

       o   Deleted data

           How many bytes of unreclaimed deleted data there are. You can
           optimize your table to minimize this space. See Section 7.6.4,
           "MyISAM Table Optimization".

       o   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 MySQL yet. For fixed tables, this is a row address.
           For dynamic tables, this is a byte address.

       o   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 MySQL. It is always a block address.

       o   Max datafile length

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

       o   Max keyfile length

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

       o   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:

       o   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 parts.

       o   Start

           Where in the row this portion of the index starts.

       o   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.

       o   Index

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

       o   Type

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

       o   Root

           Address of the root index block.

       o   Blocksize

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

       o   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 column:

       o   Field

           The column number.

       o   Start

           The byte position of the column within table rows.

       o   Length

           The length of the column in bytes.

       o   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 columns.

       o   Type

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

           o   constant

               All rows have the same value.

           o   no endspace

               Do not store endspace.

           o   no endspace, not_always

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

           o   no endspace, no empty

               Do not store endspace. Do not store empty values.

           o   table-lookup

               The column was converted to an ENUM.

           o   zerofill(N)

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

           o   no zeros

               Do not store zeros.

           o   always zero

               Zero values are stored using one bit.

       o   Huff tree

           The number of the Huffman tree associated with the column.

       o   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

       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:

       o   Data records

           The number of rows in the table.

       o   Deleted blocks

           How many deleted blocks still have reserved space. You can optimize
           your table to minimize this space. See Section 7.6.4, "MyISAM Table

       o   Key

           The key number.

       o   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).

       o   Packed

           MySQL 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

       o   Max levels

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

       o   Records

           How many rows are in the table.

       o   M.recordlength

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

       o   Packed

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

       o   Recordspace used

           What percentage of the data file is used.

       o   Empty space

           What percentage of the data file is unused.

       o   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 7.6.4,
           "MyISAM Table Optimization".

       o   Recordblocks

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

       o   Deleteblocks

           How many blocks (links) are deleted.

       o   Recorddata

           How many bytes in the data file are used.

       o   Deleted data

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

       o   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.

       o   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 512MB RAM
       available, you could use options such as these (in addition to any
       other options you might specify):

           shell> myisamchk --myisam_sort_buffer_size=256M \
                      --key_buffer_size=512M \
                      --read_buffer_size=64M \
                      --write_buffer_size=64M ...

       Using --myisam_sort_buffer_size=16M is probably enough for most cases.

       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=dir_name 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

       o   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.

       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 file system as the original data file.

       o   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=dir_name). 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 "OBTAINING
           TABLE INFORMATION WITH MYISAMCHK"). 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 (C) 1997, 2018, Oracle and/or its affiliates. All rights

       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 warranty of
       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 02110-1301 USA or see


       For more information, please refer to the MySQL Reference Manual, which
       may already be installed locally and which is also available online at


       Oracle Corporation (

MySQL 5.7                         12/20/2018                      myisamchk(1)

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