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Compressed Table Characteristics

Compressed storage format is a read-only format that is generated with the

myisampack tool.

Compressed tables can be uncompressed with myisamchk.

Compressed tables have the following characteristics:

•    Compressed tables take very little disk space. This minimizes disk usage, which is helpful when

using slow disks (such as CD-ROMs).

•    Each row is compressed separately, so there is very little access overhead. The header for a row

takes up one to three bytes depending on the biggest row 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 smali rangę, 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 rangę from -128 to 127.

•    If a column has only a smali set of possible values, the data type is converted to

ENUM.

•    A column may use any combination of the preceding compression types.

•    Can be used for fixed-length or dynamic-length rows.