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MYISAMPACK(1)		     MySQL Database System		 MYISAMPACK(1)

NAME
       myisampack - generate compressed, read-only MyISAM tables
       pack_isam - generate compressed, read-only ISAM tables

SYNOPSIS
       myisampack [options] file_name ...

       pack_isam [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.

       A similar utility, pack_isam, compresses ISAM tables. Because ISAM
       tables are deprecated, this section discusses only myisampack, but the
       general procedures for using myisampack are also true for pack_isam
       unless otherwise specified. References to myisamchk should be read as
       references to isamchk if you are using pack_isam.

       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). Allowing
	  writes to a packed table is on our TODO list, but with low priority.

       ·  myisampack can pack BLOB or TEXT columns. (The older pack_isam
	  program for ISAM tables does not have this capability.)

Invoke myisampack like this:

   shell> myisampack [options] file_name ...

Each filename argument should be the name of an index (.MYI) file. If you are
not in the database directory, you should specify the pathname 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:

·  --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 9.1, “The
   Character Set Used for Data and Sorting”.

·  --debug[=debug_options], -# [debug_options]

   Write a debugging log. The debug_options string often is ´d:t:o,file_name'.

·  --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 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).

·  --packlength=len, -p len

   Specify the row length storage size, in bytes. The value should be 1, 2, or
   3.  myisampack stores all rows with length pointers of 1, 2, or 3 bytes. In
   most normal cases, myisampack can determine the correct length value before
   it begins packing the file, but it may notice during the packing process
   that it could have used a shorter length. In this case, myisampack prints a
   note that you could use a shorter row length the next time you pack the
   same file.

·  --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, myisamchk -dvv prints 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

A similar procedure applies for ISAM tables. After using pack_isam, use
isamchk to re-create the indexes:

   shell> isamchk -rq --sort-index --analyze tbl_name.ISM

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 or isamchk.

COPYRIGHT
       Copyright 1997-2006 MySQL AB

       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 MySQL
       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 MySQL AB. MySQL AB reserves any and all rights to
       this documentation not expressly granted above.

       Please email <docs@mysql.com> for more information.

SEE ALSO
       isamchk(1), isamlog(1), msql2mysql(1), myisam_ftdump(1), myisamchk(1),
       myisamlog(1), mysql(1), mysql.server(1), mysql_config(1),
       mysql_explain_log(1), mysql_fix_privilege_tables(1), mysql_zap(1),
       mysqlaccess(1), mysqladmin(1), mysqlbinlog(1), mysqlcheck(1),
       mysqld(1), mysqld(8), mysqld_multi(1), mysqld_safe(1), mysqldump(1),
       mysqlhotcopy(1), mysqlimport(1), mysqlshow(1), pack_isam(1), perror(1),
       replace(1), safe_mysqld(1)

       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
       MySQL AB (http://www.mysql.com/).  This software comes with no
       warranty.

MySQL 4.1			  11/02/2006			 MYISAMPACK(1)
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