18.5 The ARCHIVE Storage Engine

The ARCHIVE storage engine produces special-purpose tables that store large amounts of unindexed data in a very small footprint.

Table 18.5 ARCHIVE Storage Engine Features

Feature	Support
B-tree indexes	No
Backup/point-in-time recovery (Implemented in the server, rather than in the storage engine.)	Yes
Cluster database support	No
Clustered indexes	No
Compressed data	Yes
Data caches	No
Encrypted data	Yes (Implemented in the server via encryption functions.)
Foreign key support	No
Full-text search indexes	No
Geospatial data type support	Yes
Geospatial indexing support	No
Hash indexes	No
Index caches	No
Locking granularity	Row
MVCC	No
Replication support (Implemented in the server, rather than in the storage engine.)	Yes
Storage limits	None
T-tree indexes	No
Transactions	No
Update statistics for data dictionary	Yes

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 storage engine creates files with names that begin 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, REPLACE, and SELECT, but not DELETE or UPDATE. It does support ORDER BY operations, BLOB columns, and spatial data types (see Section 13.4.1, “Spatial Data Types”). Geographic spatial reference systems are not supported. 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 statements to specify the initial sequence value for a new table or reset the sequence value for an existing table, respectively.

ARCHIVE does not support inserting a value into an AUTO_INCREMENT column less than the current maximum column value. Attempts to do so result in an ER_DUP_KEY error.

The ARCHIVE engine ignores BLOB columns if they are not requested and scans past them while reading.

The ARCHIVE storage engine does not support partitioning.

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 INSERT statement just pushes rows into a compression buffer, and that buffer flushes as necessary. The insertion into the buffer is protected by a lock. A SELECT forces a flush to occur.

• 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 SELECT never 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 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 15.7.3.4, “OPTIMIZE TABLE Statement”, Section 15.7.3.5, “REPAIR TABLE Statement”, and Section 15.7.7.38, “SHOW TABLE STATUS Statement”.

Additional Resources

• A forum dedicated to the ARCHIVE storage engine is available at https://forums.mysql.com/list.php?112.