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FreeBSD/Linux/UNIX General Commands Manual
Hypertext Man Pages
myisampack
 
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:

       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.

       o  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:

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

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

       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 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).

       o  --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.

       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 myisamchk 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, myisamchk -dvv prints 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

       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.

SEE ALSO
       isamchk(1), isamlog(1), msql2mysql(1), myisamchk(1), myisamlog(1),
       mysql(1), mysql.server(1), mysql_config(1),
       mysql_fix_privilege_tables(1), mysql_zap(1), mysqlaccess(1),
       mysqladmin(1), mysqlbinlog(1), mysqlcheck(1), mysqld(1),
       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			  01/27/2006			 MYISAMPACK(1)
=30089
+45
(5)