14.6. 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 14.10. ARCHIVE Storage EngineFeatures

Storage limits None Transactions No Locking granularity Table
MVCC No Geospatial data type support Yes Geospatial indexing support No
B-tree indexes No T-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 engine.

[c] Implemented in the server, rather than in the storage engine.

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, "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:

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, "OPTIMIZE TABLE Syntax", Section, "REPAIR TABLE Syntax", and Section, "SHOW TABLE STATUS Syntax".

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