The ARCHIVE storage engine is used for storing
large amounts of data without indexes in a very small footprint.
The ARCHIVE storage engine is included in MySQL
binary distributions. To enable this storage engine if you build
MySQL from source, invoke configure with the
--with-archive-storage-engine option.
To examine the source for the ARCHIVE engine,
look in the sql directory of a MySQL source
distribution.
You can check whether the ARCHIVE storage
engine is available with this statement:
mysql> SHOW VARIABLES LIKE 'have_archive';
When you create an ARCHIVE table, the server
creates a table format file in the database directory. The file
begins with the table name and has an .frm
extension. The storage engine creates other files, all having
names beginning with the table name. The data and metadata files
have extensions of .ARZ and
.ARM, respectively. An
.ARN file may appear during optimization
operations.
The ARCHIVE engine supports
INSERT and SELECT, but not
DELETE, REPLACE, or
UPDATE. It does support ORDER
BY operations, BLOB columns, and
basically all but spatial data types (see
Section 16.4.1, “MySQL Spatial Data Types”). The
ARCHIVE engine uses row-level locking.
Storage: Rows are compressed as
they are inserted. The ARCHIVE engine uses
zlib lossless data compression (see
http://www.zlib.net/). You can use
OPTIMIZE TABLE to analyze the table and pack it
into a smaller format (for a reason to use OPTIMIZE
TABLE, see later in this section). Beginning with MySQL
5.0.15, the engine also supports CHECK TABLE.
There are several types of insertions that are used:
-
An
INSERTstatement just pushes rows into a compression buffer, and that buffer flushes as necessary. The insertion into the buffer is protected by a lock. ASELECTforces a flush to occur, unless the only insertions that have come in wereINSERT DELAYED(those flush as necessary). See Section 13.2.4.2, “INSERT DELAYEDSyntax”. -
A bulk insert is visible only after it completes, unless other inserts occur at the same time, in which case it can be seen partially. A
SELECTnever causes a flush of a bulk insert unless a normal insert occurs while it is loading.
Retrieval: On retrieval, rows are
uncompressed on demand; there is no row cache. A
SELECT operation performs a complete table
scan: When a SELECT occurs, it finds out how
many rows are currently available and reads that number of rows.
SELECT is performed as a consistent read. Note
that lots of SELECT statements during insertion
can deteriorate the compression, unless only bulk or delayed
inserts are used. To achieve better compression, you can use
OPTIMIZE TABLE or REPAIR
TABLE. The number of rows in ARCHIVE
tables reported by SHOW TABLE STATUS is always
accurate. See Section 13.5.2.5, “OPTIMIZE TABLE Syntax”,
Section 13.5.2.6, “REPAIR TABLE Syntax”, and
Section 13.5.4.21, “SHOW TABLE STATUS Syntax”.
Additional resources
-
A forum dedicated to the
ARCHIVEstorage engine is available at http://forums.mysql.com/list.php?112.