myisamchk(1)


NAME

   myisamchk - MyISAM table-maintenance utility

SYNOPSIS

   myisamchk [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 that have .MYD and .MYI files for storing data and indexes).

   The use of myisamchk with partitioned tables is not supported.

       Caution
       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 \
                 /path/to/datadir/*/*.MYI

   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".

       Important
       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 on.

       Otherwise, when you run myisamchk, it may display the following
       error message:

           warning: clients are using or havent 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 hasnt
       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.

MYISAMCHK GENERAL OPTIONS

   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 d:t:o,/tmp/myisamchk.trace.

   *   --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 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.

MYISAMCHK CHECK OPTIONS

   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.

       For a description of the output format, see the section called
       "MYISAMCHK TABLE INFORMATION".

   *   --fast, -F

       Check only tables that havent 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 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 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 shouldnt
       use this option if the mysqld server is using the table and you are
       running it with external locking disabled.

MYISAMCHK REPAIR OPTIONS

   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 called
       "MYISAMCHK TABLE INFORMATION".

   *   --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
       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 --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
       key_buffer_size.

   *   --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.

OTHER MYISAMCHK OPTIONS

   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 TABLE INFORMATION".

   *   --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
       tables index numbers, use SHOW INDEX, which displays a tables
       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 "nulls_ignored".

MYISAMCHK TABLE INFORMATION

   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 tables 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 address.

   *   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 keys 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.

   *   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 column:

   *   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 columns.

   *   Type

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

       *   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 length.

   *   Packed

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

   *   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.

MYISAMCHK MEMORY USAGE

   Memory allocation is important when you run myisamchk.  myisamchk uses
   no more memory than its memory-related variables are set to. If you are
   going to use myisamchk on very large tables, you should first decide
   how much memory you want it to use. The default is to use only about
   3MB to perform repairs. By using larger values, you can get myisamchk
   to operate faster. For example, if you have more than 32MB RAM, you
   could use options such as these (in addition to any other options you
   might specify):

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

   Using --sort_buffer_size=16M should probably be enough for most cases.

   Be aware that myisamchk uses temporary files in TMPDIR. If TMPDIR
   points to a memory 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 file.

   *   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

   Copyright 2007-2008 MySQL AB, 2008-2010 Sun Microsystems, Inc.,
   2010-2015 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 warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. 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 02110-1301 USA or see
   http://www.gnu.org/licenses/.

SEE ALSO

   For more information, please refer to the MariaDB Knowledge Base,
   available online at https://mariadb.com/kb/

AUTHOR

   MariaDB Foundation (http://www.mariadb.org/).





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