Provided by: mysql-server-core-8.0_8.0.31-0ubuntu2_amd64 bug

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).

       •   myisampack does not support partitioned tables.

       Invoke myisampack like this:

           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, 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 4.2.2.3, “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=dir_name The directory where character sets are installed. See
           Section 10.15, “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.

           This option is available only if MySQL was built using WITH_DEBUG. MySQL release
           binaries provided by Oracle are not built using this option.

       •   --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.

       •   --silent, -s Silent mode. Write output only when errors occur.

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

       •   --tmpdir=dir_name, -T dir_name 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:

           $> ls -l station.*
           -rw-rw-r--   1 jones    my         994128 Apr 17 19:00 station.MYD
           -rw-rw-r--   1 jones    my          53248 Apr 17 19:00 station.MYI
           $> 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
           $> 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
           $> myisamchk -rq station
           - check record delete-chain
           - recovering (with sort) MyISAM-table 'station'
           Data records: 1192
           - Fixing index 1
           - Fixing index 2
           $> mysqladmin -uroot flush-tables
           $> ls -l station.*
           -rw-rw-r--   1 jones    my         127874 Apr 17 19:00 station.MYD
           -rw-rw-r--   1 jones    my          55296 Apr 17 19:04 station.MYI
           $> 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, use 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:

           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, 2022, Oracle and/or its affiliates.

       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 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/).