| MYISAMPACK(1) | MariaDB 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:
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”.
Display a help message and exit.
Make a backup of each table's data file using the name tbl_name.OLD.
The directory where character sets are installed. See Section 9.5, “Character Set Configuration”.
Write a debugging log. A typical debug_options string is 'd:t:o,file_name'. The default is 'd:t:o'.
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 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.
Silent mode. Write output only when errors occur.
Do not actually pack the table, just test packing it.
Use the named directory as the location where myisampack creates temporary files.
Verbose mode. Write information about the progress of the packing operation and its result.
Display version information and exit.
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.frmshell> myisamchk -dvv stationMyISAM file: stationIsam-version: 2Creation time: 1996-03-13 10:08:58Recover time: 1997-02-02 3:06:43Data records: 1192 Deleted blocks: 0Datafile parts: 1192 Deleted data: 0Datafile pointer (bytes): 2 Keyfile pointer (bytes): 2Max datafile length: 54657023 Max keyfile length: 33554431Recordlength: 834Record format: Fixed lengthtable description:Key Start Len Index Type Root Blocksize Rec/key1 2 4 unique unsigned long 1024 1024 12 32 30 multip. text 10240 1024 1Field Start Length Type1 1 12 2 43 6 44 10 15 11 206 31 17 32 308 62 359 97 3510 132 3511 167 412 171 1613 187 3514 222 415 226 1616 242 2017 262 2018 282 2019 302 3020 332 421 336 422 340 123 341 824 349 825 357 826 365 227 367 228 369 429 373 430 377 131 378 232 380 833 388 434 392 435 396 436 400 437 404 138 405 439 409 440 413 441 417 442 421 443 425 444 429 2045 449 3046 479 147 480 148 481 7949 560 7950 639 7951 718 7952 797 853 805 154 806 155 807 2056 827 457 831 4shell> myisampack station.MYICompressing station.MYI: (1192 records)- Calculating statisticsnormal: 20 empty-space: 16 empty-zero: 12 empty-fill: 11pre-space: 0 end-space: 12 table-lookups: 5 zero: 7Original trees: 57 After join: 17- Compressing file87.14%Remember to run myisamchk -rq on compressed tablesshell> 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.frmshell> myisamchk -dvv stationMyISAM file: stationIsam-version: 2Creation time: 1996-03-13 10:08:58Recover time: 1997-04-17 19:04:26Data records: 1192 Deleted blocks: 0Datafile parts: 1192 Deleted data: 0Datafile pointer (bytes): 3 Keyfile pointer (bytes): 1Max datafile length: 16777215 Max keyfile length: 131071Recordlength: 834Record format: Compressedtable description:Key Start Len Index Type Root Blocksize Rec/key1 2 4 unique unsigned long 10240 1024 12 32 30 multip. text 54272 1024 1Field Start Length Type Huff tree Bits1 1 1 constant 1 02 2 4 zerofill(1) 2 93 6 4 no zeros, zerofill(1) 2 94 10 1 3 95 11 20 table-lookup 4 06 31 1 3 97 32 30 no endspace, not_always 5 98 62 35 no endspace, not_always, no empty 6 99 97 35 no empty 7 910 132 35 no endspace, not_always, no empty 6 911 167 4 zerofill(1) 2 912 171 16 no endspace, not_always, no empty 5 913 187 35 no endspace, not_always, no empty 6 914 222 4 zerofill(1) 2 915 226 16 no endspace, not_always, no empty 5 916 242 20 no endspace, not_always 8 917 262 20 no endspace, no empty 8 918 282 20 no endspace, no empty 5 919 302 30 no endspace, no empty 6 920 332 4 always zero 2 921 336 4 always zero 2 922 340 1 3 923 341 8 table-lookup 9 024 349 8 table-lookup 10 025 357 8 always zero 2 926 365 2 2 927 367 2 no zeros, zerofill(1) 2 928 369 4 no zeros, zerofill(1) 2 929 373 4 table-lookup 11 030 377 1 3 931 378 2 no zeros, zerofill(1) 2 932 380 8 no zeros 2 933 388 4 always zero 2 934 392 4 table-lookup 12 035 396 4 no zeros, zerofill(1) 13 936 400 4 no zeros, zerofill(1) 2 937 404 1 2 938 405 4 no zeros 2 939 409 4 always zero 2 940 413 4 no zeros 2 941 417 4 always zero 2 942 421 4 no zeros 2 943 425 4 always zero 2 944 429 20 no empty 3 945 449 30 no empty 3 946 479 1 14 447 480 1 14 448 481 79 no endspace, no empty 15 949 560 79 no empty 2 950 639 79 no empty 2 951 718 79 no endspace 16 952 797 8 no empty 2 953 805 1 17 154 806 1 3 955 807 20 no empty 3 956 827 4 no zeros, zerofill(2) 2 957 831 4 no zeros, zerofill(1) 2 9
myisampack displays the following kinds of information:
The number of columns for which no extra packing is used.
The number of columns containing values that are only spaces. These occupy one bit.
The number of columns containing values that are only binary zeros. These occupy one bit.
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.
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.
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.
The column had only a small number of different values, which were converted to an ENUM before Huffman compression.
The number of columns for which all values are zero.
The initial number of Huffman trees.
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:
The data type. The value may contain any of the following descriptors:
All rows have the same value.
Do not store endspace.
Do not store endspace and do not do endspace compression for all values.
Do not store endspace. Do not store empty values.
The column was converted to an ENUM.
The most significant N bytes in the value are always 0 and are not stored.
Do not store zeros.
Zero values are stored using one bit.
The number of the Huffman tree associated with the column.
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., 2010-2020 MariaDB Foundation
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 02110-1335 USA or see http://www.gnu.org/licenses/.
SEE ALSO
For more information, please refer to the MariaDB Knowledge Base, available online at https://mariadb.com/kb/
AUTHOR
MariaDB Foundation (http://www.mariadb.org/).
| 15 May 2020 | MariaDB 10.11 |