MySQL Reference Manual for version 4.0.18.
14.1.2.3 Compressed Table Characteristics
This is a read-only type that is generated with the optional
myisampack tool (pack_isam for ISAM tables):
-
All MySQL distributions, even those that existed before MySQL
went
GPL, can read tables that were compressed with myisampack.
-
Compressed tables take very little disk space. This minimises disk usage, which
is very nice when using slow disks (such as CD-ROMs).
-
Each record is compressed separately (very little access overhead). The
header for a record is fixed (1-3 bytes) depending on the biggest record in the
table. Each column is compressed differently. Some of the compression types
are:
-
There is usually a different Huffman table for each column.
-
Suffix space compression.
-
Prefix space compression.
-
Numbers with value
0 are stored using 1 bit.
-
If values in an integer column have a small range, the column is stored using
the smallest possible type. For example, a
BIGINT column (8 bytes) may
be stored as a TINYINT column (1 byte) if all values are in the range
0 to 255.
-
If a column has only a small set of possible values, the column type is
converted to
ENUM.
-
A column may use a combination of the above compressions.
-
Can handle fixed- or dynamic-length records.
-
Can be uncompressed with
myisamchk.
This document was generated
by rdg (Feb 25 2004)
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