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 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. (Prior to MySQL 5.1.15, a metadata file with an extension of .ARM is created as well.) 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 11.13.4.1, “MySQL Spatial Data Types”). The ARCHIVE engine uses row-level locking.

As of MySQL 5.1.6, 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.

As of MySQL 5.1.6, the ARCHIVE engine ignores BLOB columns if they are not requested and scans past them while reading. Formerly, the following two statements had the same cost, but as of 5.1.6, the second is much more efficient than the first:

SELECT a, b, blob_col FROM archive_table;
SELECT a, b FROM archive_table;

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 12.4.2.5, “OPTIMIZE TABLE Syntax”, Section 12.4.2.6, “REPAIR TABLE Syntax”, and Section 12.4.5.38, “SHOW TABLE STATUS Syntax”.

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