# myisampack

## 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%–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.
    
           MariaDB uses mmap() when possible to perform memory mapping on
           compressed tables. If mmap() does not work, MariaDB falls back to
           normal read/write file operations.
    
           Please note the following:
    
           •   If the **mariadbd** 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 **mariadbd** 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 MariaDB optimizer to work more
           efficiently:
    
               shell> **myisamchk -rq --sort-index --analyze** _tbl_name_**.MYI**
    
           After you have installed the packed table into the MariaDB
           database directory, you should execute **mariadb-admin flush-tables**
           to force **mariadbd** to start using the new table.
    
           To unpack a packed table, use the **--unpack** option to **myisamchk**.
    


* * *