(mysql.info.gz) Compressed format
Info Catalog
(mysql.info.gz) Dynamic format
(mysql.info.gz) MyISAM table formats
14.1.3.3 Compressed Table Characteristics
.........................................
Compressed storage format is a read-only format that is generated with
the `myisampack' tool.
All MySQL distributions as of version 3.23.19 include `myisampack' by
default. (This version is when MySQL was placed under the GPL.) For
earlier versions, `myisampack' was included only with licenses or
support agreements, but the server still can read tables that were
compressed with `myisampack'. Compressed tables can be uncompressed
with `myisamchk'. (For the `ISAM' storage engine, compressed tables
can be created with `pack_isam' and uncompressed with `isamchk'.)
Compressed tables have the following characteristics:
* Compressed tables take very little disk space. This minimizes disk
usage, which is very nice when using slow disks (such as CD-ROMs).
* Each record is compressed separately, so there is 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. There is usually a different Huffman tree
for each column. Some of the compression types are:
- Suffix space compression.
- Prefix space compression.
- Numbers with a value of zero are stored using one 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 (eight bytes) can be stored as a `TINYINT'
column (one byte) if all its values are in the range from
`-128' to `127'.
- 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 preceding compressions.
* Can handle fixed-length or dynamic-length records.
Info Catalog
(mysql.info.gz) Dynamic format
(mysql.info.gz) MyISAM table formats
automatically generated byinfo2html