Compressed Table Characteristics-opracowanie

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 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.
... zobacz całą notatkę