The ARCHIVE storage engine is used for storing
large amounts of data without indexes in a very small footprint.
Table 13.13. ARCHIVE Storage Engine
Features
| Storage limits | None | Transactions | No | Locking granularity | Row |
| MVCC | No | Geospatial data type support | Yes | Geospatial indexing support | No |
| B-tree indexes | No | Hash indexes | No | Full-text search indexes | No |
| Clustered indexes | No | Data caches | No | Index caches | No |
| Compressed data | Yes | Encrypted data[a] | Yes | Cluster database support | No |
| Replication support[b] | Yes | Foreign key support | No | Backup / point-in-time recovery[c] | Yes |
| Query cache support | Yes | Update statistics for data dictionary | Yes | ||
[a] Implemented in the server (via encryption functions), rather than in the storage engine. [b] Implemented in the server, rather than in the storage product [c] Implemented in the server, rather than in the storage product | |||||
The ARCHIVE storage engine is included in MySQL
binary distributions. To enable this storage engine if you build
MySQL from source, invoke CMake with the
-DWITH_ARCHIVE_STORAGE_ENGINE
option.
To examine the source for the ARCHIVE engine,
look in the storage/archive directory of a
MySQL source distribution.
You can check whether the ARCHIVE storage engine
is available with the SHOW ENGINES
statement.
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 file has an extension of
.ARZ. 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 11.17.4.1, “MySQL Spatial Data Types”).
The ARCHIVE engine uses row-level locking.
The ARCHIVE engine supports the
AUTO_INCREMENT column attribute. The
AUTO_INCREMENT column can have either a unique or
nonunique index. Attempting to create an index on any other column
results in an error. The ARCHIVE engine also
supports the AUTO_INCREMENT table option in
CREATE TABLE and
ALTER TABLE statements to specify the
initial sequence value for a new table or reset the sequence value
for an existing table, respectively.
The ARCHIVE engine ignores
BLOB columns if they are not
requested and scans past them while reading.
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). 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 12.2.5.2, “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 12.4.2.4, “OPTIMIZE TABLE Syntax”,
Section 12.4.2.5, “REPAIR TABLE Syntax”, and
Section 12.4.5.37, “SHOW TABLE STATUS Syntax”.
Additional Resources
A forum dedicated to the
ARCHIVEstorage engine is available at http://forums.mysql.com/list.php?112.