MYISAMPACK(1)

NAME
myisampack - generate compressed, read-only MyISAM tables

SYNOPSIS

myisampack [options] file_name ...

DESCRIPTION

The myisampack utility compresses MyISAM tables. myisampack works by compressing each column in the table separately. Usually, myisampack packs the data file 40% to 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 4.2.3.4, “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 10.5, “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

Copyright © 1997, 2013, Oracle and/or its affiliates. All rights reserved.

This software and related documentation are provided under a license agreement containing restrictions on use and disclosure and are protected by intellectual property laws. Except as expressly permitted in your license agreement or allowed by law, you may not use, copy, reproduce, translate, broadcast, modify, license, transmit, distribute, exhibit, perform, publish, or display any part, in any form, or by any means. Reverse engineering, disassembly, or decompilation of this software, unless required by law for interoperability, is prohibited.

The information contained herein is subject to change without notice and is not warranted to be error-free. If you find any errors, please report them to us in writing.

If this software or related documentation is delivered to the U.S. Government or anyone licensing it on behalf of the U.S. Government, the following notice is applicable:

U.S. GOVERNMENT RIGHTS Programs, software, databases, and related documentation and technical data delivered to U.S. Government customers are "commercial computer software" or "commercial technical data" pursuant to the applicable Federal Acquisition Regulation and agency-specific supplemental regulations. As such, the use, duplication, disclosure, modification, and adaptation shall be subject to the restrictions and license terms set forth in the applicable Government contract, and, to the extent applicable by the terms of the Government contract, the additional rights set forth in FAR 52.227-19, Commercial Computer Software License (December 2007). Oracle USA, Inc., 500 Oracle Parkway, Redwood City, CA 94065.

This software is developed for general use in a variety of information management applications. It is not developed or intended for use in any inherently dangerous applications, including applications which may create a risk of personal injury. If you use this software in dangerous applications, then you shall be responsible to take all appropriate fail-safe, backup, redundancy, and other measures to ensure the safe use of this software. Oracle Corporation and its affiliates disclaim any liability for any damages caused by use of this software in dangerous applications.

Oracle is a registered trademark of Oracle Corporation and/or its affiliates. MySQL is a trademark of Oracle Corporation and/or its affiliates, and shall not be used without Oracle's express written authorization. Other names may be trademarks of their respective owners.

This software and documentation may provide access to or information on content, products, and services from third parties. Oracle Corporation and its affiliates are not responsible for and expressly disclaim all warranties of any kind with respect to third-party content, products, and services. Oracle Corporation and its affiliates will not be responsible for any loss, costs, or damages incurred due to your access to or use of third-party content, products, or services.

This document in any form, software or printed matter, contains proprietary information that is the exclusive property of Oracle. Your access to and use of this material is subject to the terms and conditions of your Oracle Software License and Service Agreement, which has been executed and with which you agree to comply. This document and information contained herein may not be disclosed, copied, reproduced, or distributed to anyone outside Oracle without prior written consent of Oracle or as specifically provided below. This document is not part of your license agreement nor can it be incorporated into any contractual agreement with Oracle or its subsidiaries or affiliates.

This documentation is NOT distributed under a GPL license. Use of this documentation is subject to the following terms:

You may create a printed copy of this documentation solely for your own personal use. Conversion to other formats is allowed as long as the actual content is not altered or edited in any way. You shall not publish or distribute this documentation in any form or on any media, except if you distribute the documentation in a manner similar to how Oracle disseminates it (that is, electronically for download on a Web site with the software) or on a CD-ROM or similar medium, provided however that the documentation is disseminated together with the software on the same medium. Any other use, such as any dissemination of printed copies or use of this documentation, in whole or in part, in another publication, requires the prior written consent from an authorized representative of Oracle. Oracle and/or its affiliates reserve any and all rights to this documentation not expressly granted above.

For more information on the terms of this license, or for details on how the MySQL documentation is built and produced, please visit MySQL Contact & Questions.

For additional licensing information, including licenses for third-party libraries used by MySQL products, see Preface and Legal Notices.

For help with using MySQL, please visit either the MySQL Forums or MySQL Mailing Lists where you can discuss your issues with other MySQL users.

For additional documentation on MySQL products, including translations of the documentation into other languages, and downloadable versions in variety of formats, including HTML and PDF formats, see the MySQL Documentation Library.

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

AUTHOR
Oracle Corporation (http://dev.mysql.com/).