Redistributes data across the nodes in a nodegroup. The current data distribution, whether it is uniform or skewed, can be specified. The redistribution algorithm selects the partitions to be moved based on the current data distribution.
This command can only be issued from the catalog node. Use LIST DATABASE DIRECTORY to determine which node is the catalog node for each database.
Scope
This command affects all nodes in the nodegroup.
Authorization
One of the following:
Command Syntax
>>-REDISTRIBUTE NODEGROUP--nodegroup---------------------------->
>-----+-+-UNIFORM-------------------+-+------------------------><
| '-USING DISTFILE--distfile--' |
+-USING TARGETMAP--targetmap----+
+-CONTINUE----------------------+
'-ROLLBACK----------------------'
Command Parameters
| Note: | Tables in the IBMCATGROUP and the IBMTEMPGROUP nodegroups cannot be redistributed. |
Use the distfile to indicate the current distribution of data across the 4 096 hash partitions.
Use row counts, byte volumes, or any other measure to indicate the amount of data represented by each hash partition. The utility reads the integer value associated with a partition as the weight of that partition. When a distfile is specified, the utility generates a target partitioning map that it uses to redistribute the data across the nodes in the nodegroup as uniformly as possible. After the redistribution, the weight of each node in the nodegroup is approximately the same (the weight of a node is the sum of the weights of all partitions that map to that node).
For example, the input distribution file may contain entries as follows:
10223 1345 112000 0 100 ...
In the example, hash partition 2 has a weight of 112 000, and partition 3 (with a weight of 0) has no data mapping to it at all.
The distfile should contain 4 096 positive integer values in character format. The sum of the values should be less than or equal to 4 294 967 295.
If the path for distfile is not specified, the current directory is used.
If a node included in the target map is not in the nodegroup, an error is returned. Issue ALTER NODEGROUP ADD NODE before running REDISTRIBUTE NODEGROUP.
If a node excluded from the target map is in the nodegroup, that node will not be included in the partitioning. Such a node can be dropped using ALTER NODEGROUP DROP NODE either before or after REDISTRIBUTE NODEGROUP.
Usage Notes
When a redistribution operation is done, a message file is written to:
The time stamp value is the time when the command was issued.
This utility performs intermittent COMMITs during processing.
Use the ALTER NODEGROUP statement to add nodes to a nodegroup. This statement permits one to define the containers for the table spaces associated with the nodegroup. See the SQL Reference for details.
| Note: | DB2 Parallel Edition for AIX Version 1 syntax, with ADD NODE and DROP NODE options, is supported for users with sysadm or sysctrl authority. For ADD NODE, containers are created like the containers on the lowest node number of the existing nodes within the nodegroup. |
All packages having a dependency on a table that has undergone redistribution are invalidated. It is recommended to explicitly rebind such packages after the redistribute nodegroup operation has completed. Explicit rebinding eliminates the initial delay in the execution of the first SQL request for the invalid package. The redistribute message file contains a list of all the tables that have undergone redistribution.
It is also recommended to update statistics by issuing RUNSTATS after the redistribute nodegroup operation has completed.
Nodegroups containing replicated summary tables or tables defined with DATA CAPTURE CHANGES cannot be redistributed.
See Also