myisampack


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:

       o   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.

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

       o   myisampack does not support partitioned tables.

       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, 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 4.2.7, "Command-Line Options that Affect Option-File Handling".

       o   --help, -?

           Display a help message and exit.

       o   --backup, -b

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

           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.

       o   --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.

       o   --silent, -s

           Silent mode. Write output only when errors occur.

       o   --test, -t

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

       o   --tmpdir=dir_name, -T dir_name

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

       o   --verbose, -v

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

       o   --version, -V

           Display version information and exit.

       o   --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.*
           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
           - 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> myisamchk -rq station
           - check record delete-chain
           - recovering (with sort) MyISAM-table 'station'
           Data records: 1192
           - Fixing index 1
           - Fixing index 2
           shell> mysqladmin -uroot flush-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
           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:

       o   normal

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

       o   empty-space

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

       o   empty-zero

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

       o   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.

       o   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

       o   zero

           The number of columns for which all values are zero.

       o   Original trees

           The initial number of Huffman trees.

       o   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:

       o   Type

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

           o   constant

               All rows have the same value.

           o   no endspace

               Do not store endspace.

           o   no endspace, not_always

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

           o   no endspace, no empty

               Do not store endspace. Do not store empty values.

           o   table-lookup

               The column was converted to an ENUM.

           o   zerofill(N)

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

           o   no zeros

               Do not store zeros.

           o   always zero

       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 (C) 1997, 2016, Oracle and/or its affiliates. All rights
       reserved.

       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/).



MySQL 5.5                         11/26/2016                     MYISAMPACK(1)
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