MYISAMPACK(1)						       MySQL Database System						     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%-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). Allowing writes
	   to a packed table is on our TODO list, but with low priority.

       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".

       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.

       o   --character-sets-dir=path

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

       o   --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'.

       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.

       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. 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.

       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=path, -T path

	   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.*
	   -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:

       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
	   spaces.

       o   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.

       o   table-lookup

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

       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

	       Zero values are stored using one bit.

       o   Huff tree

	   The number of the Huffman tree associated with the column.

       o   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 2007-2008 MySQL AB, 2008-2010 Sun Microsystems, Inc.

       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

       Sun Microsystems, Inc. (http://www.mysql.com/).

MySQL 5.1							    04/06/2010							     MYISAMPACK(1)