1MYISAMPACK(1)                MySQL Database System               MYISAMPACK(1)
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3
4

NAME

6       myisampack - generate compressed, read-only MyISAM tables
7

SYNOPSIS

9       myisampack [options] file_name ...
10

DESCRIPTION

12       The myisampack utility compresses MyISAM tables.  myisampack works by
13       compressing each column in the table separately. Usually, myisampack
14       packs the data file 40% to 70%.
15
16       When the table is used later, the server reads into memory the
17       information needed to decompress columns. This results in much better
18       performance when accessing individual rows, because you only have to
19       uncompress exactly one row.
20
21       MySQL uses mmap() when possible to perform memory mapping on compressed
22       tables. If mmap() does not work, MySQL falls back to normal read/write
23       file operations.
24
25       Please note the following:
26
27       ·   If the mysqld server was invoked with external locking disabled, it
28           is not a good idea to invoke myisampack if the table might be
29           updated by the server during the packing process. It is safest to
30           compress tables with the server stopped.
31
32       ·   After packing a table, it becomes read only. This is generally
33           intended (such as when accessing packed tables on a CD).
34
35       ·   myisampack does not support partitioned tables.
36
37       Invoke myisampack like this:
38
39           shell> myisampack [options] file_name ...
40
41       Each file name argument should be the name of an index (.MYI) file. If
42       you are not in the database directory, you should specify the path name
43       to the file. It is permissible to omit the .MYI extension.
44
45       After you compress a table with myisampack, use myisamchk -rq to
46       rebuild its indexes.  myisamchk(1).
47
48       myisampack supports the following options. It also reads option files
49       and supports the options for processing them described at
50       Section 4.2.2.3, “Command-Line Options that Affect Option-File
51       Handling”.
52
53       ·   --help, -?  Display a help message and exit.
54
55       ·   --backup, -b Make a backup of each table's data file using the name
56           tbl_name.OLD.
57
58       ·   --character-sets-dir=dir_name The directory where character sets
59           are installed. See Section 10.15, “Character Set Configuration”.
60
61       ·   --debug[=debug_options], -# [debug_options] Write a debugging log.
62           A typical debug_options string is d:t:o,file_name. The default is
63           d:t:o.
64
65           This option is available only if MySQL was built using WITH_DEBUG.
66           MySQL release binaries provided by Oracle are not built using this
67           option.
68
69       ·   --force, -f Produce a packed table even if it becomes larger than
70           the original or if the intermediate file from an earlier invocation
71           of myisampack exists. (myisampack creates an intermediate file
72           named tbl_name.TMD in the database directory while it compresses
73           the table. If you kill myisampack, the .TMD file might not be
74           deleted.) Normally, myisampack exits with an error if it finds that
75           tbl_name.TMD exists. With --force, myisampack packs the table
76           anyway.
77
78       ·   --join=big_tbl_name, -j big_tbl_name Join all tables named on the
79           command line into a single packed table big_tbl_name. All tables
80           that are to be combined must have identical structure (same column
81           names and types, same indexes, and so forth).
82
83           big_tbl_name must not exist prior to the join operation. All source
84           tables named on the command line to be merged into big_tbl_name
85           must exist. The source tables are read for the join operation but
86           not modified.
87
88       ·   --silent, -s Silent mode. Write output only when errors occur.
89
90       ·   --test, -t Do not actually pack the table, just test packing it.
91
92       ·   --tmpdir=dir_name, -T dir_name Use the named directory as the
93           location where myisampack creates temporary files.
94
95       ·   --verbose, -v Verbose mode. Write information about the progress of
96           the packing operation and its result.
97
98       ·   --version, -V Display version information and exit.
99
100       ·   --wait, -w Wait and retry if the table is in use. If the mysqld
101           server was invoked with external locking disabled, it is not a good
102           idea to invoke myisampack if the table might be updated by the
103           server during the packing process.
104
105       The following sequence of commands illustrates a typical table
106       compression session:
107
108           shell> ls -l station.*
109           -rw-rw-r--   1 jones    my         994128 Apr 17 19:00 station.MYD
110           -rw-rw-r--   1 jones    my          53248 Apr 17 19:00 station.MYI
111           shell> myisamchk -dvv station
112           MyISAM file:     station
113           Isam-version:  2
114           Creation time: 1996-03-13 10:08:58
115           Recover time:  1997-02-02  3:06:43
116           Data records:              1192  Deleted blocks:              0
117           Datafile parts:            1192  Deleted data:                0
118           Datafile pointer (bytes):     2  Keyfile pointer (bytes):     2
119           Max datafile length:   54657023  Max keyfile length:   33554431
120           Recordlength:               834
121           Record format: Fixed length
122           table description:
123           Key Start Len Index   Type                 Root  Blocksize    Rec/key
124           1   2     4   unique  unsigned long        1024       1024          1
125           2   32    30  multip. text                10240       1024          1
126           Field Start Length Type
127           1     1     1
128           2     2     4
129           3     6     4
130           4     10    1
131           5     11    20
132           6     31    1
133           7     32    30
134           8     62    35
135           9     97    35
136           10    132   35
137           11    167   4
138           12    171   16
139           13    187   35
140           14    222   4
141           15    226   16
142           16    242   20
143           17    262   20
144           18    282   20
145           19    302   30
146           20    332   4
147           21    336   4
148           22    340   1
149           23    341   8
150           24    349   8
151           25    357   8
152           26    365   2
153           27    367   2
154           28    369   4
155           29    373   4
156           30    377   1
157           31    378   2
158           32    380   8
159           33    388   4
160           34    392   4
161           35    396   4
162           36    400   4
163           37    404   1
164           38    405   4
165           39    409   4
166           40    413   4
167           41    417   4
168           42    421   4
169           43    425   4
170           44    429   20
171           45    449   30
172           46    479   1
173           47    480   1
174           48    481   79
175           49    560   79
176           50    639   79
177           51    718   79
178           52    797   8
179           53    805   1
180           54    806   1
181           55    807   20
182           56    827   4
183           57    831   4
184           shell> myisampack station.MYI
185           Compressing station.MYI: (1192 records)
186           - Calculating statistics
187           normal:     20  empty-space:   16  empty-zero:     12  empty-fill:  11
188           pre-space:   0  end-space:     12  table-lookups:   5  zero:         7
189           Original trees:  57  After join: 17
190           - Compressing file
191           87.14%
192           Remember to run myisamchk -rq on compressed tables
193           shell> myisamchk -rq station
194           - check record delete-chain
195           - recovering (with sort) MyISAM-table 'station'
196           Data records: 1192
197           - Fixing index 1
198           - Fixing index 2
199           shell> mysqladmin -uroot flush-tables
200           shell> ls -l station.*
201           -rw-rw-r--   1 jones    my         127874 Apr 17 19:00 station.MYD
202           -rw-rw-r--   1 jones    my          55296 Apr 17 19:04 station.MYI
203           shell> myisamchk -dvv station
204           MyISAM file:     station
205           Isam-version:  2
206           Creation time: 1996-03-13 10:08:58
207           Recover time:  1997-04-17 19:04:26
208           Data records:               1192  Deleted blocks:              0
209           Datafile parts:             1192  Deleted data:                0
210           Datafile pointer (bytes):      3  Keyfile pointer (bytes):     1
211           Max datafile length:    16777215  Max keyfile length:     131071
212           Recordlength:                834
213           Record format: Compressed
214           table description:
215           Key Start Len Index   Type                 Root  Blocksize    Rec/key
216           1   2     4   unique  unsigned long       10240       1024          1
217           2   32    30  multip. text                54272       1024          1
218           Field Start Length Type                         Huff tree  Bits
219           1     1     1      constant                             1     0
220           2     2     4      zerofill(1)                          2     9
221           3     6     4      no zeros, zerofill(1)                2     9
222           4     10    1                                           3     9
223           5     11    20     table-lookup                         4     0
224           6     31    1                                           3     9
225           7     32    30     no endspace, not_always              5     9
226           8     62    35     no endspace, not_always, no empty    6     9
227           9     97    35     no empty                             7     9
228           10    132   35     no endspace, not_always, no empty    6     9
229           11    167   4      zerofill(1)                          2     9
230           12    171   16     no endspace, not_always, no empty    5     9
231           13    187   35     no endspace, not_always, no empty    6     9
232           14    222   4      zerofill(1)                          2     9
233           15    226   16     no endspace, not_always, no empty    5     9
234           16    242   20     no endspace, not_always              8     9
235           17    262   20     no endspace, no empty                8     9
236           18    282   20     no endspace, no empty                5     9
237           19    302   30     no endspace, no empty                6     9
238           20    332   4      always zero                          2     9
239           21    336   4      always zero                          2     9
240           22    340   1                                           3     9
241           23    341   8      table-lookup                         9     0
242           24    349   8      table-lookup                        10     0
243           25    357   8      always zero                          2     9
244           26    365   2                                           2     9
245           27    367   2      no zeros, zerofill(1)                2     9
246           28    369   4      no zeros, zerofill(1)                2     9
247           29    373   4      table-lookup                        11     0
248           30    377   1                                           3     9
249           31    378   2      no zeros, zerofill(1)                2     9
250           32    380   8      no zeros                             2     9
251           33    388   4      always zero                          2     9
252           34    392   4      table-lookup                        12     0
253           35    396   4      no zeros, zerofill(1)               13     9
254           36    400   4      no zeros, zerofill(1)                2     9
255           37    404   1                                           2     9
256           38    405   4      no zeros                             2     9
257           39    409   4      always zero                          2     9
258           40    413   4      no zeros                             2     9
259           41    417   4      always zero                          2     9
260           42    421   4      no zeros                             2     9
261           43    425   4      always zero                          2     9
262           44    429   20     no empty                             3     9
263           45    449   30     no empty                             3     9
264           46    479   1                                          14     4
265           47    480   1                                          14     4
266           48    481   79     no endspace, no empty               15     9
267           49    560   79     no empty                             2     9
268           50    639   79     no empty                             2     9
269           51    718   79     no endspace                         16     9
270           52    797   8      no empty                             2     9
271           53    805   1                                          17     1
272           54    806   1                                           3     9
273           55    807   20     no empty                             3     9
274           56    827   4      no zeros, zerofill(2)                2     9
275           57    831   4      no zeros, zerofill(1)                2     9
276
277       myisampack displays the following kinds of information:
278
279       ·   normal
280
281           The number of columns for which no extra packing is used.
282
283       ·   empty-space
284
285           The number of columns containing values that are only spaces. These
286           occupy one bit.
287
288       ·   empty-zero
289
290           The number of columns containing values that are only binary zeros.
291           These occupy one bit.
292
293       ·   empty-fill
294
295           The number of integer columns that do not occupy the full byte
296           range of their type. These are changed to a smaller type. For
297           example, a BIGINT column (eight bytes) can be stored as a TINYINT
298           column (one byte) if all its values are in the range from -128 to
299           127.
300
301       ·   pre-space
302
303           The number of decimal columns that are stored with leading spaces.
304           In this case, each value contains a count for the number of leading
305           spaces.
306
307       ·   end-space
308
309           The number of columns that have a lot of trailing spaces. In this
310           case, each value contains a count for the number of trailing
311           spaces.
312
313       ·   table-lookup
314
315           The column had only a small number of different values, which were
316           converted to an ENUM before Huffman compression.
317
318       ·   zero
319
320           The number of columns for which all values are zero.
321
322       ·   Original trees
323
324           The initial number of Huffman trees.
325
326       ·   After join
327
328           The number of distinct Huffman trees left after joining trees to
329           save some header space.
330
331       After a table has been compressed, the Field lines displayed by
332       myisamchk -dvv include additional information about each column:
333
334       ·   Type
335
336           The data type. The value may contain any of the following
337           descriptors:
338
339           ·   constant
340
341               All rows have the same value.
342
343           ·   no endspace
344
345               Do not store endspace.
346
347           ·   no endspace, not_always
348
349               Do not store endspace and do not do endspace compression for
350               all values.
351
352           ·   no endspace, no empty
353
354               Do not store endspace. Do not store empty values.
355
356           ·   table-lookup
357
358               The column was converted to an ENUM.
359
360           ·   zerofill(N)
361
362               The most significant N bytes in the value are always 0 and are
363               not stored.
364
365           ·   no zeros
366
367               Do not store zeros.
368
369           ·   always zero
370
371               Zero values are stored using one bit.
372
373       ·   Huff tree
374
375           The number of the Huffman tree associated with the column.
376
377       ·   Bits
378
379           The number of bits used in the Huffman tree.
380
381       After you run myisampack, use myisamchk to re-create any indexes. At
382       this time, you can also sort the index blocks and create statistics
383       needed for the MySQL optimizer to work more efficiently:
384
385           shell> myisamchk -rq --sort-index --analyze tbl_name.MYI
386
387       After you have installed the packed table into the MySQL database
388       directory, you should execute mysqladmin flush-tables to force mysqld
389       to start using the new table.
390
391       To unpack a packed table, use the --unpack option to myisamchk.
392
394       Copyright © 1997, 2020, Oracle and/or its affiliates.
395
396       This documentation is free software; you can redistribute it and/or
397       modify it only under the terms of the GNU General Public License as
398       published by the Free Software Foundation; version 2 of the License.
399
400       This documentation is distributed in the hope that it will be useful,
401       but WITHOUT ANY WARRANTY; without even the implied warranty of
402       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
403       General Public License for more details.
404
405       You should have received a copy of the GNU General Public License along
406       with the program; if not, write to the Free Software Foundation, Inc.,
407       51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA or see
408       http://www.gnu.org/licenses/.
409
410

SEE ALSO

412       For more information, please refer to the MySQL Reference Manual, which
413       may already be installed locally and which is also available online at
414       http://dev.mysql.com/doc/.
415

AUTHOR

417       Oracle Corporation (http://dev.mysql.com/).
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421MySQL 8.0                         11/26/2020                     MYISAMPACK(1)
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