Administration Guide

Chapter 18. Redistributing Data Across Database Partitions

Only if you are working in a partitioned database environment do you need to be concerned with redistribution of data. If you are in a single partition database environment there is no need for you to use the information found here.

You use the Data Redistribution utility to move data among the database partitions in an existing nodegroup. You can use it to do the following:

• Balance data volumes and processing loads across database partitions.

  This is useful if you have a database table in which all the data is accessed on a regular basis.

• Introduce skew in the data distribution across database partitions.

  This is useful if you have a database table in which only some of the data is accessed on a regular basis. In this situation, you could redistribute the table so that the infrequently accessed data is on a small number of database partitions in the nodegroup, and the frequently accessed data is distributed over a larger number of partitions. This would improve access performance and throughput on the most frequently run applications.

• Add database partitions to a nodegroup. (Provided for backward compatibility only with DB2 for Parallel Edition. The recommended way to add a database partition is to use the ALTER NODEGROUP command.)

• Drop database partitions from a nodegroup. (Provided for backward compatibility only with DB2 for Parallel Edition. The recommended way to drop a database partition is to use the ALTER NODEGROUP command.)

To preserve table collocation, this operation is applied to all tables in a nodegroup, and redistribution is done at the nodegroup level rather than at the table level.

To achieve the data distribution that you want, the utility uses a partitioning map to move the rows of the tables among the database partitions of the nodegroup. Depending on the option you specify, the utility can generate a target partitioning map or can use an existing partitioning map as input.

Notes:

1. You should specify a log file size based on the log space requirements you think that the Data Redistribution operation will need. You should also ensure that the log is large enough to accommodate the INSERT and DELETE operations done at each database partition where data is being redistributed.

2. If you want to redistribute the data in a nodegroup that contains replicated summary tables, you must first drop these tables, redistribute the nodegroup, then re-create the tables. You cannot redistribute a nodegroup that contains replicated summary tables.

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