MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6
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:
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).
myisampack does not support partitioned tables.
Invoke myisampack like this:
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, use myisamchk -rq to rebuild its indexes. Section 4.6.3, “myisamchk — MyISAM Table-Maintenance Utility”.
myisampack supports the following options. It also reads option files and supports the options for processing them described at Section 4.2.2.3, “Command-Line Options that Affect Option-File Handling”.
--help,
-?
| Command-Line Format | --help |
|---|
Display a help message and exit.
--backup,
-b
| Command-Line Format | --backup |
|---|
Make a backup of each table's data file using the name
tbl_name.OLD
| Command-Line Format | --character-sets-dir=dir_name |
|---|---|
| Type | Directory name |
The directory where character sets are installed. See Section 10.15, “Character Set Configuration”.
--debug[=,
debug_options]-#
[
debug_options]
| Command-Line Format | --debug[=debug_options] |
|---|---|
| Type | String |
| Default Value | d:t:o |
Write a debugging log. A typical
debug_options string is
d:t:o,.
The default is file_named:t:o.
This option is available only if MySQL was built using
WITH_DEBUG. MySQL release
binaries provided by Oracle are not
built using this option.
--force,
-f
| Command-Line Format | --force |
|---|
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.TMD file might not be deleted.)
Normally, myisampack exits with an error
if it finds that
tbl_name.TMD--force,
myisampack packs the table anyway.
--join=,
big_tbl_name-j
big_tbl_name
| Command-Line Format | --join=big_tbl_name |
|---|---|
| Type | String |
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.
--silent,
-s
| Command-Line Format | --silent |
|---|
Silent mode. Write output only when errors occur.
--test,
-t
| Command-Line Format | --test |
|---|
Do not actually pack the table, just test packing it.
--tmpdir=,
dir_name-T
dir_name
| Command-Line Format | --tmpdir=dir_name |
|---|---|
| Type | Directory name |
Use the named directory as the location where myisampack creates temporary files.
--verbose,
-v
| Command-Line Format | --verbose |
|---|
Verbose mode. Write information about the progress of the packing operation and its result.
--version,
-V
| Command-Line Format | --version |
|---|
Display version information and exit.
--wait,
-w
| Command-Line Format | --wait |
|---|
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:
$>ls -l station.*-rw-rw-r-- 1 jones my 994128 Apr 17 19:00 station.MYD -rw-rw-r-- 1 jones my 53248 Apr 17 19:00 station.MYI -rw-rw-r-- 1 jones my 5767 Apr 17 19:00 station.frm $>myisamchk -dvv stationMyISAM 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 $>myisampack station.MYICompressing 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 $>myisamchk -rq station- check record delete-chain - recovering (with sort) MyISAM-table 'station' Data records: 1192 - Fixing index 1 - Fixing index 2 $>mysqladmin -uroot flush-tables$>ls -l station.*-rw-rw-r-- 1 jones my 127874 Apr 17 19:00 station.MYD -rw-rw-r-- 1 jones my 55296 Apr 17 19:04 station.MYI -rw-rw-r-- 1 jones my 5767 Apr 17 19:00 station.frm $>myisamchk -dvv stationMyISAM 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:
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
All rows have the same value.
no endspace
Do not store endspace.
no endspace, not_always
Do not store endspace and do not do endspace compression for all values.
no endspace, no empty
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, use 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:
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.