Spec-Zone .ru
спецификации, руководства, описания, API
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Spec-Zone .ru
спецификации, руководства, описания, API
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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 |
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[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. |
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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
12.18.4.1, "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
). 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 13.2.5.2, "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 13.7.2.4, "OPTIMIZE
TABLE Syntax", Section 13.7.2.5, "REPAIR
TABLE Syntax", and Section 13.7.5.37, "SHOW TABLE STATUS Syntax".
A forum dedicated to the ARCHIVE storage engine is
available at .