15.5 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 15.5 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 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
, REPLACE
, and SELECT
, but not DELETE
or UPDATE
. It does support ORDER BY
operations, BLOB
columns, and basically all data types including spatial data types (see Section 11.4.1, “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.
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. ASELECT
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 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 Statement”, Section 13.7.2.5, “REPAIR TABLE Statement”, and Section 13.7.5.36, “SHOW TABLE STATUS Statement”.
Additional Resources
A forum dedicated to the
ARCHIVE
storage engine is available at https://forums.mysql.com/list.php?112 .