INIT CXX/FXX/IXX/LXX/WXX/Data Area › INIT IXX (Format Index Area) › When to Use › Controlling the Index Block Size

Controlling the Index Block Size

The block size of each database Index Area (IXX) and index partition area (Inn) is determined during IXX (or Inn) initialization. When you initialize an index area, you can override the default index block size by using the optional BLKSIZE= keyword. BLKSIZE= can be used to specify an index block size of from 4096 bytes through 8192 bytes. The BLKSIZE= value remains in effect until the next initialization of the index area. Pick an optimal size for your device type, in a manner similar to how the data area block size is selected.

The index block size default provided by CA Datacom can be changed by the DBIN1PR function DEFAULT to be a different value. For details about INIT_IXX_BLKSIZE=, see DEFAULT. Any change in default is documented in a console message and in the report, but then allows execution without it being considered an error.

The index block size has the ability to be forced to a specific value even if specified on the function by the DBIN1PR function FORCE to be a different value. For details about INIT_IXX_BLKSIZE=, see FORCE. Any force is documented in a console message and in the report, but then allows execution without it being considered an error.

Note: We do not recommend using a block size other than the default. Changing the block size might help in the use of some parts of index storage and processing, but other parts could be hurt by the change. Therefore, changing the block size should only be done after first experimenting to discover whether the change causes better or worse results. Be aware that the index can double in size using 8K blocks when OLDEP= is not specified as NO.

The index is complex and proprietary, typically involving various key lengths, degrees of compression, and the possibility of from one to many duplicate values. Different combinations could therefore increase or decrease DASD usage, and could also, independently, increase or decrease CPU usage. This is why we caution you that, if you want to try to improve resource use by changing the index block size from the default, experimentation is needed to find out what results a change in block size has with regard to the mix of applications, CPU availability, and DASD availability.

Note: An OPEN error occurs if an attempt is made to open a database that has an index block size larger than the index buffer size. For more information about the ixxbfrsize parameter of the SYSPOOL MUF startup option, see CA Datacom/DB Database and System Administration Guide.