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:
· 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.
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
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 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
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.*
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
· 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
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
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
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