New Storage Engines in MySQL 5

MySQL 5 offers a number of new storage engines (previously
called table types). In addition to the default MyISAM storage engine, and the InnoDB,
BDB, HEAP and MERGE storage engines, there are four new types: CSV, ARCHIVE,
FEDERATED and EXAMPLE, as well as a new name for the HEAP storage engine. It is
now called the MEMORY storage engine. None of the new types are available by
default – you can check for sure with the SHOW ENGINES statement. Here is what
is on my default version of MySQL Max:

mysql> SHOW ENGINES;
+------------+---------+------------------------------------------------------------+
| Engine     | Support | Comment                                                    |
+------------+---------+------------------------------------------------------------+
| MyISAM     | DEFAULT | Default engine as of MySQL 3.23 with great performance     |
| HEAP       | YES     | Alias for MEMORY                                           |
| MEMORY     | YES     | Hash based, stored in memory, useful for temporary tables  |
| MERGE      | YES     | Collection of identical MyISAM tables                      |
| MRG_MYISAM | YES     | Alias for MERGE                                            |
| ISAM       | NO      | Obsolete storage engine, now replaced by MyISAM            |
| MRG_ISAM   | NO      | Obsolete storage engine, now replaced by MERGE             |
| InnoDB     | YES     | Supports transactions, row-level locking, and foreign keys |
| INNOBASE   | YES     | Alias for INNODB                                           |
| BDB        | YES     | Supports transactions and page-level locking               |
| BERKELEYDB | YES     | Alias for BDB                                              |
| NDBCLUSTER | NO      | Clustered, fault-tolerant, memory-based tables             |
| NDB        | NO      | Alias for NDBCLUSTER                                       |
| EXAMPLE    | NO      | Example storage engine                                     |
| ARCHIVE    | NO      | Archive storage engine                                     |
| CSV        | NO      | CSV storage engine                                         |
+------------+---------+------------------------------------------------------------+

To add
support for the missing storage engines, you currently need to build MySQL with
certain options. It is likely though that there will be binary versions that
include these storage engines by default at some point. Until then, there is no
other way to enable them.

Changes in the MEMORY storage engine

You can read my article on the HEAP table type as a start, as most of the detail has not
changed, and refer below for modifications in MySQL 5.

Previously, the HEAP storage engine only made use of hash indexes. These allow
finding specific matches extremely quickly, but do not return any kind of range
data. An index matches a record, but there is no ordering to allow it to return
subsequent records. Only the complete index can be used, the concept of
leftmost prefixing (using the left part of an index) does not apply. The MEMORY
storage engine now permits BTREE indexes as well (the kind used by MyISAM
tables by default).

To specify an index type, use the USING clause, as in the following examples:

CREATE TABLE memory_table (f1 INT, INDEX USING BTREE (f1)) ENGINE = MEMORY;

or:

CREATE TABLE memory_table (f1 INT, INDEX USING HASH (f1)) ENGINE = MEMORY;

The HASH index is still the default, and will be the type of
index created if you do not specify a particular kind.

• Now support AUTO_INCREMENT
• Now support INSERT DELAYED
• Support indexes on columns that can contain NULL values
• Never get converted to disk tables. (Temporary internal tables
  are automatically converted to disk table if they get too big, MEMORY tables
  never are. The max_heap_table_size variable (it hasn’t yet changed its
  name to reflect the new storage engine name) places a limit on the memory utilization
  of MEMORY tables, and you can always place a MAX_ROWS limit as well, when
  creating the table.

The EXAMPLE storage engine

Added in MySQL 4.1.3 and only
of interest to developers, the EXAMPLE storage engine does nothing, but is
there to provide simple source code for developers to base new storage engines
on. For those interested, the source code can be found in the sql/examples
directory.

The FEDERATED storage engine

Added in MySQL 5.0.3, to make
use of it you need to use the –with-federated-storage-engine option to
configure when building MySQL. The FEDERATED storage engine allows you to
access data from a table on another database server. That table can make use of
any storage engine. Let’s see it in action. First, CREATE a table on a remote
server (you can do this on the same server for testing purposes, but doing so is
fairly pointless otherwise).

CREATE TABLE myisam_table (f1 INT, PRIMARY KEY(f1)) 
ENGINE=MYISAM;

Assuming that the default is
set to create MyISAM tables (FEDERATED tables can access tables of any type),
the above statement creates a definition file (.frm), an index file (.MYI) and
a data file (.MYD). If you had created an InnoDB file, MySQL would create a
definition (.frm) and index and data file (.idb). Now create the FEDERATED
table on another server. The original table must always exist first:

CREATE TABLE federated_table (f1 INT, PRIMARY KEY(f1)) 
ENGINE=FEDERATED 
COMMENT='mysql://username:[email protected]:3306/dbname/myisam_table';