myisampack(1) — Linux manual page

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MYISAMPACK(1)            MariaDB Database System           MYISAMPACK(1)

NAME         top

       myisampack - generate compressed, read-only MyISAM tables

SYNOPSIS         top

       myisampack [options] file_name ...

DESCRIPTION         top

       The myisampack utility compresses MyISAM tables.  myisampack
       works by compressing each column in the table separately.
       Usually, myisampack packs the data file 40%–70%.

       When the table is used later, the server reads into memory the
       information needed to decompress columns. This results in much
       better performance when accessing individual rows, because you
       only have to uncompress exactly one row.

       MySQL uses mmap() when possible to perform memory mapping on
       compressed tables. If mmap() does not work, MySQL falls back to
       normal read/write file operations.

       Please note the following:

       •   If the mysqld server was invoked with external locking
           disabled, it is not a good idea to invoke myisampack if the
           table might be updated by the server during the packing
           process. It is safest to compress tables with the server
           stopped.

       •   After packing a table, it becomes read only. This is
           generally intended (such as when accessing packed tables on a
           CD).

       Invoke myisampack like this:

           shell> myisampack [options] file_name ...

       Each file name argument should be the name of an index (.MYI)
       file. If you are not in the database directory, you should
       specify the path name to the file. It is permissible to omit the
       .MYI extension.

       After you compress a table with myisampack, you should use
       myisamchk -rq to rebuild its indexes.  myisamchk(1).

       myisampack supports the following options. It also reads option
       files and supports the options for processing them described at
       Section 4.2.3.3.1, “Command-Line Options that Affect Option-File
       Handling”.

       •   --help, -?

           Display a help message and exit.

       •   --backup, -b

           Make a backup of each table´s data file using the name
           tbl_name.OLD.

       •   --character-sets-dir=path

           The directory where character sets are installed. See
           Section 9.5, “Character Set Configuration”.

       •   --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´.

       •   --force, -f

           Produce a packed table even if it becomes larger than the
           original or if the intermediate file from an earlier
           invocation of myisampack exists. (myisampack creates an
           intermediate file named tbl_name.TMD in the database
           directory while it compresses the table. If you kill
           myisampack, the .TMD file might not be deleted.) Normally,
           myisampack exits with an error if it finds that tbl_name.TMD
           exists. With --force, myisampack packs the table anyway.

       •   --join=big_tbl_name, -j big_tbl_name

           Join all tables named on the command line into a single
           packed table big_tbl_name. All tables that are to be combined
           must have identical structure (same column names and types,
           same indexes, and so forth).

           big_tbl_name must not exist prior to the join operation. All
           source tables named on the command line to be merged into
           big_tbl_name must exist. The source tables are read for the
           join operation but not modified. The join operation does not
           create a .frm file for big_tbl_name, so after the join
           operation finishes, copy the .frm file from one of the source
           tables and name it big_tbl_name.frm.

       •   --silent, -s

           Silent mode. Write output only when errors occur.

       •   --test, -t

           Do not actually pack the table, just test packing it.

       •   --tmpdir=path, -T path

           Use the named directory as the location where myisampack
           creates temporary files.

       •   --verbose, -v

           Verbose mode. Write information about the progress of the
           packing operation and its result.

       •   --version, -V

           Display version information and exit.

       •   --wait, -w

           Wait and retry if the table is in use. If the mysqld server
           was invoked with external locking disabled, it is not a good
           idea to invoke myisampack if the table might be updated by
           the server during the packing process.

       The following sequence of commands illustrates a typical table
       compression session:

           shell> ls -l station.*
           -rw-rw-r--   1 monty    my         994128 Apr 17 19:00 station.MYD
           -rw-rw-r--   1 monty    my          53248 Apr 17 19:00 station.MYI
           -rw-rw-r--   1 monty    my           5767 Apr 17 19:00 station.frm
           shell> myisamchk -dvv station
           MyISAM file:     station
           Isam-version:  2
           Creation time: 1996-03-13 10:08:58
           Recover time:  1997-02-02  3:06:43
           Data records:              1192  Deleted blocks:              0
           Datafile parts:            1192  Deleted data:                0
           Datafile pointer (bytes):     2  Keyfile pointer (bytes):     2
           Max datafile length:   54657023  Max keyfile length:   33554431
           Recordlength:               834
           Record format: Fixed length
           table description:
           Key Start Len Index   Type                 Root  Blocksize    Rec/key
           1   2     4   unique  unsigned long        1024       1024          1
           2   32    30  multip. text                10240       1024          1
           Field Start Length Type
           1     1     1
           2     2     4
           3     6     4
           4     10    1
           5     11    20
           6     31    1
           7     32    30
           8     62    35
           9     97    35
           10    132   35
           11    167   4
           12    171   16
           13    187   35
           14    222   4
           15    226   16
           16    242   20
           17    262   20
           18    282   20
           19    302   30
           20    332   4
           21    336   4
           22    340   1
           23    341   8
           24    349   8
           25    357   8
           26    365   2
           27    367   2
           28    369   4
           29    373   4
           30    377   1
           31    378   2
           32    380   8
           33    388   4
           34    392   4
           35    396   4
           36    400   4
           37    404   1
           38    405   4
           39    409   4
           40    413   4
           41    417   4
           42    421   4
           43    425   4
           44    429   20
           45    449   30
           46    479   1
           47    480   1
           48    481   79
           49    560   79
           50    639   79
           51    718   79
           52    797   8
           53    805   1
           54    806   1
           55    807   20
           56    827   4
           57    831   4
           shell> myisampack station.MYI
           Compressing station.MYI: (1192 records)
           - Calculating statistics
           normal:     20  empty-space:   16  empty-zero:     12  empty-fill:  11
           pre-space:   0  end-space:     12  table-lookups:   5  zero:         7
           Original trees:  57  After join: 17
           - Compressing file
           87.14%
           Remember to run myisamchk -rq on compressed tables
           shell> ls -l station.*
           -rw-rw-r--   1 monty    my         127874 Apr 17 19:00 station.MYD
           -rw-rw-r--   1 monty    my          55296 Apr 17 19:04 station.MYI
           -rw-rw-r--   1 monty    my           5767 Apr 17 19:00 station.frm
           shell> myisamchk -dvv station
           MyISAM file:     station
           Isam-version:  2
           Creation time: 1996-03-13 10:08:58
           Recover time:  1997-04-17 19:04:26
           Data records:               1192  Deleted blocks:              0
           Datafile parts:             1192  Deleted data:                0
           Datafile pointer (bytes):      3  Keyfile pointer (bytes):     1
           Max datafile length:    16777215  Max keyfile length:     131071
           Recordlength:                834
           Record format: Compressed
           table description:
           Key Start Len Index   Type                 Root  Blocksize    Rec/key
           1   2     4   unique  unsigned long       10240       1024          1
           2   32    30  multip. text                54272       1024          1
           Field Start Length Type                         Huff tree  Bits
           1     1     1      constant                             1     0
           2     2     4      zerofill(1)                          2     9
           3     6     4      no zeros, zerofill(1)                2     9
           4     10    1                                           3     9
           5     11    20     table-lookup                         4     0
           6     31    1                                           3     9
           7     32    30     no endspace, not_always              5     9
           8     62    35     no endspace, not_always, no empty    6     9
           9     97    35     no empty                             7     9
           10    132   35     no endspace, not_always, no empty    6     9
           11    167   4      zerofill(1)                          2     9
           12    171   16     no endspace, not_always, no empty    5     9
           13    187   35     no endspace, not_always, no empty    6     9
           14    222   4      zerofill(1)                          2     9
           15    226   16     no endspace, not_always, no empty    5     9
           16    242   20     no endspace, not_always              8     9
           17    262   20     no endspace, no empty                8     9
           18    282   20     no endspace, no empty                5     9
           19    302   30     no endspace, no empty                6     9
           20    332   4      always zero                          2     9
           21    336   4      always zero                          2     9
           22    340   1                                           3     9
           23    341   8      table-lookup                         9     0
           24    349   8      table-lookup                        10     0
           25    357   8      always zero                          2     9
           26    365   2                                           2     9
           27    367   2      no zeros, zerofill(1)                2     9
           28    369   4      no zeros, zerofill(1)                2     9
           29    373   4      table-lookup                        11     0
           30    377   1                                           3     9
           31    378   2      no zeros, zerofill(1)                2     9
           32    380   8      no zeros                             2     9
           33    388   4      always zero                          2     9
           34    392   4      table-lookup                        12     0
           35    396   4      no zeros, zerofill(1)               13     9
           36    400   4      no zeros, zerofill(1)                2     9
           37    404   1                                           2     9
           38    405   4      no zeros                             2     9
           39    409   4      always zero                          2     9
           40    413   4      no zeros                             2     9
           41    417   4      always zero                          2     9
           42    421   4      no zeros                             2     9
           43    425   4      always zero                          2     9
           44    429   20     no empty                             3     9
           45    449   30     no empty                             3     9
           46    479   1                                          14     4
           47    480   1                                          14     4
           48    481   79     no endspace, no empty               15     9
           49    560   79     no empty                             2     9
           50    639   79     no empty                             2     9
           51    718   79     no endspace                         16     9
           52    797   8      no empty                             2     9
           53    805   1                                          17     1
           54    806   1                                           3     9
           55    807   20     no empty                             3     9
           56    827   4      no zeros, zerofill(2)                2     9
           57    831   4      no zeros, zerofill(1)                2     9

       myisampack displays the following kinds of information:

       •   normal

           The number of columns for which no extra packing is used.

       •   empty-space

           The number of columns containing values that are only spaces.
           These occupy one bit.

       •   empty-zero

           The number of columns containing values that are only binary
           zeros. These occupy one bit.

       •   empty-fill

           The number of integer columns that do not occupy the full
           byte range of their type. These are changed to a smaller
           type. For example, a BIGINT column (eight bytes) can be
           stored as a TINYINT column (one byte) if all its values are
           in the range from -128 to 127.

       •   pre-space

           The number of decimal columns that are stored with leading
           spaces. In this case, each value contains a count for the
           number of leading spaces.

       •   end-space

           The number of columns that have a lot of trailing spaces. In
           this case, each value contains a count for the number of
           trailing spaces.

       •   table-lookup

           The column had only a small number of different values, which
           were converted to an ENUM before Huffman compression.

       •   zero

           The number of columns for which all values are zero.

       •   Original trees

           The initial number of Huffman trees.

       •   After join

           The number of distinct Huffman trees left after joining trees
           to save some header space.

       After a table has been compressed, the Field lines displayed by
       myisamchk -dvv include additional information about each column:

       •   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.

       After you run myisampack, you must run myisamchk to re-create any
       indexes. At this time, you can also sort the index blocks and
       create statistics needed for the MySQL optimizer to work more
       efficiently:

           shell> myisamchk -rq --sort-index --analyze tbl_name.MYI

       After you have installed the packed table into the MySQL database
       directory, you should execute mysqladmin flush-tables to force
       mysqld to start using the new table.

       To unpack a packed table, use the --unpack option to myisamchk.

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
       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
       02110-1335 USA or see http://www.gnu.org/licenses/.

SEE ALSO         top

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

AUTHOR         top

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

COLOPHON         top

       This page is part of the MariaDB (MariaDB database server)
       project.  Information about the project can be found at 
       ⟨http://mariadb.org/⟩.  If you have a bug report for this manual
       page, see ⟨https://mariadb.com/kb/en/mariadb/reporting-bugs/⟩.
       This page was obtained from the project's upstream Git repository
       ⟨https://github.com/MariaDB/server⟩ on 2021-08-27.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2021-08-26.)  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
       man-pages@man7.org

MariaDB 10.6                   15 May 2020                 MYISAMPACK(1)

Pages that refer to this page: aria_pack(1)myisamchk(1)