13.1.14 CREATE LOGFILE GROUP Syntax

CREATE LOGFILE GROUP logfile_group
    ADD UNDOFILE 'undo_file'
    [INITIAL_SIZE [=] initial_size]
    [UNDO_BUFFER_SIZE [=] undo_buffer_size]
    [REDO_BUFFER_SIZE [=] redo_buffer_size]
    [NODEGROUP [=] nodegroup_id]
    [WAIT]
    [COMMENT [=] comment_text]
    ENGINE [=] engine_name

This statement creates a new log file group named logfile_group having a single UNDO file named 'undo_file'. A CREATE LOGFILE GROUP statement has one and only one ADD UNDOFILE clause. For rules covering the naming of log file groups, see Section 9.2, “Schema Object Names”.

Note

All MySQL Cluster Disk Data objects share the same namespace. This means that each Disk Data object must be uniquely named (and not merely each Disk Data object of a given type). For example, you cannot have a tablespace and a log file group with the same name, or a tablespace and a data file with the same name.

Beginning with MySQL 5.1.8, you can have only one log file group per Cluster at any given time. (See Bug #16386)

Prior to MySQL Cluster NDB 6.2.17, 6.3.23, and 6.4.3, path and file names for undo log files could not be longer than 128 characters. (Bug #31769)

The optional INITIAL_SIZE parameter sets the UNDO file's initial size; if not specified, it defaults to 128M (128 megabytes). The optional UNDO_BUFFER_SIZE parameter sets the size used by the UNDO buffer for the log file group; The default value for UNDO_BUFFER_SIZE is 8M (eight megabytes); this value cannot exceed the amount of system memory available. Both of these parameters are specified in bytes. You may optionally follow either or both of these with a one-letter abbreviation for an order of magnitude, similar to those used in my.cnf. Generally, this is one of the letters M (for megabytes) or G (for gigabytes).

The memory used for both INITIAL_SIZE and UNDO_BUFFER_SIZE comes from the global pool whose size is determined by the value of the SharedGlobalMemory data node configuration parameter. This includes any default value implied for these options by the setting of the InitialLogFileGroup data node configuration parameter.

Beginning with MySQL Cluster NDB 6.2.17, 6.3.23, and 6.4.3, the maximum permitted for UNDO_BUFFER_SIZE is 600M; previously, it was 150M. (Bug #34102)

On 32-bit systems, the maximum supported value for INITIAL_SIZE is 4G. (Bug #29186)

Beginning with MySQL Cluster NDB 2.1.18, 6.3.24, and 7.0.4, the minimum permitted value for INITIAL_SIZE is 1M. (Bug #29574)

The ENGINE option determines the storage engine to be used by this log file group, with engine_name being the name of the storage engine. In MySQL 5.1, this must be NDB (or NDBCLUSTER). If ENGINE is not set, MySQL tries to use the engine specified by the storage_engine server system variable. In any case, if the engine is not specified as NDB or NDBCLUSTER, the CREATE LOGFILE GROUP statement appears to succeed but actually fails to create the log file group, as shown here:

mysql> CREATE LOGFILE GROUP lg1 
    ->     ADD UNDOFILE 'undo.dat' INITIAL_SIZE = 10M;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> SHOW WARNINGS;
+-------+------+------------------------------------------------------------------------------------------------+
| Level | Code | Message                                                                                        |
+-------+------+------------------------------------------------------------------------------------------------+
| Error | 1478 | Table storage engine 'MyISAM' does not support the create option 'TABLESPACE or LOGFILE GROUP' |
+-------+------+------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> DROP LOGFILE GROUP lg1 ENGINE = NDB;              
ERROR 1529 (HY000): Failed to drop LOGFILE GROUP

mysql> CREATE LOGFILE GROUP lg1 
    ->     ADD UNDOFILE 'undo.dat' INITIAL_SIZE = 10M
    ->     ENGINE = NDB;
Query OK, 0 rows affected (2.97 sec)

The fact that the CREATE LOGFILE GROUP statement does not actually return an error when a non-NDB storage engine is named, but rather appears to succeed, is a known issue which we hope to address in a future release of MySQL Cluster.

REDO_BUFFER_SIZE, NODEGROUP, WAIT, and COMMENT are parsed but ignored, and so have no effect in MySQL 5.1. These options are intended for future expansion.

When used with ENGINE [=] NDB, a log file group and associated UNDO log file are created on each Cluster data node. You can verify that the UNDO files were created and obtain information about them by querying the INFORMATION_SCHEMA.FILES table. For example:

mysql> SELECT LOGFILE_GROUP_NAME, LOGFILE_GROUP_NUMBER, EXTRA
    -> FROM INFORMATION_SCHEMA.FILES
    -> WHERE FILE_NAME = 'undo_10.dat';
+--------------------+----------------------+----------------+
| LOGFILE_GROUP_NAME | LOGFILE_GROUP_NUMBER | EXTRA          |
+--------------------+----------------------+----------------+
| lg_3               |                   11 | CLUSTER_NODE=3 |
| lg_3               |                   11 | CLUSTER_NODE=4 |
+--------------------+----------------------+----------------+
2 rows in set (0.06 sec)

CREATE LOGFILE GROUP was added in MySQL 5.1.6. In MySQL 5.1, it is useful only with Disk Data storage for MySQL Cluster. See Section 17.5.12, “MySQL Cluster Disk Data Tables”.