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% to 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 (C) 1997, 2010, Oracle and/or its affiliates. All rights
reserved.
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
Oracle Corporation (http://dev.mysql.com/).