13.12. The ARCHIVE Storage Engine

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 limitsNoneTransactionsNoLocking granularityRow
MVCCNoGeospatial data type supportYesGeospatial indexing supportNo
B-tree indexesNoHash indexesNoFull-text search indexesNo
Clustered indexesNoData cachesNoIndex cachesNo
Compressed dataYesEncrypted data[a]YesCluster database supportNo
Replication support[b]YesForeign key supportNoBackup / point-in-time recovery[c]Yes
Query cache supportYesUpdate statistics for data dictionaryYes  

[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 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, unless the only insertions that have come in were INSERT DELAYED (those flush as necessary). See Section 12.2.5.2, “INSERT DELAYED Syntax”.

  • 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 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”.

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