New features in Release 7.2.1.3-P1

Random chunk distribution

The maximum number of non-empty tables on the system depends on the table row counts and widths and on the number of extents that the tables use. Release 7.2.1.3-P1 introduces a feature for storing user tables that are created as DISTRIBUTE ON RANDOM so that the overall number of user tables on the system can be increased. This feature, called random chunk distribution, optimizes the disk space (extent) utilization. This feature intentionally skews the storage of the records for a table to one or a very few extents. Using a minimal number of extents reduces the allocated storage for tables, which allows users to create more small tables. With this feature, users can create as many as 200,000 non-empty tables, or even more.

The random chunk distribution feature is disabled by default. To enable the feature, use the system.enableRandomDistributionChunkSize system registry variable. It requires a pause and resume of the system to take effect. The feature does not change the behavior for tables that are distributed on 1 - 4 specific columns (hash distributions).

User tables that take advantage of the chunk distributions might appear on the skew reports. Because these tables are typically small tables, you can ignore them as part of your table skew investigations.

For more information, see the section on random chunk distributions in the IBM Netezza System Administrator’s Guide.

System and session configuration settings

Release 7.2.1.3-P1 introduces the following configuration settings to support the random chunk distribution feature:

• The system.enableRandomDistributionChunkSize system registry variable enables or disables the random chunk distribution feature at the system-wide level. If the value of the system.enableRandomDistributionChunkSize registry variable is yes or on and users specify DISTRIBUTE ON RANDOM when creating tables, the system uses random chunk distribution to store records for the tables. The default value of the system.enableRandomDistributionChunkSize registry variable is no (off).
• If you set the enable_random_dist_chunk session variable to no or off (for example, specify set enable_random_dist_chunk = no), it disables the random chunk distribution feature at the session level if the value of the system.enableRandomDistributionChunkSize registry variable is yes or on. The default value of the enable_random_dist_chunk session variable is yes (on). If the value of the system.enableRandomDistributionChunkSize registry variable is no or off, setting the enable_random_dist_chunk session variable to yes or on has no effect.