14.1.3.3. 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).
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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 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 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.
