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16.5 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 16.5 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 storage
engine creates files with names that begin 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 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.
The ARCHIVE
storage engine does not support
partitioning.
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 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 13.7.3.4, “OPTIMIZE TABLE
Statement”, Section 13.7.3.5, “REPAIR TABLE
Statement”, and Section 13.7.7.36, “SHOW TABLE
STATUS Statement”.
Additional Resources
-
A forum dedicated to the
ARCHIVE
storage engine is available at https://forums.mysql.com/list.php?112.