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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 11.5.1, “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 Syntax”,
Section 13.7.3.5, “REPAIR TABLE Syntax”, and
Section 13.7.6.36, “SHOW TABLE STATUS Syntax”.
Additional Resources
A forum dedicated to the
ARCHIVE
storage engine is available at https://forums.mysql.com/list.php?112.
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