Best Practices for SAP BI using DB2 9 for z/OS - IBM Redbooks

added. If you do not manage PSA properly, you may have too many partitions
and wasted storage space for a new load. A best practice is to reclaim usage of
space occupied by obsolete data in the PSA. Reuse of the same number of
partitions is greatly facilitated by DB2 partition rotation. Partition rotation is the
process whereby the number of partitions is kept the same, but the oldest
partition now becomes the newest. Essentially, this occurs when the old data is
archived or deleted and the space is now required for reuse.
Note that SAP BW has a PSA tablespace created with default option
COMPRESS YES, which results in DB2 data compression. Data loaded into the
PSA is often repeated character strings, so storage size usage benefits from
compression. In addition to the storage space usage benefit, performance
benefits from data transfer with less I/O activities, improving utilization of the
buffer pool, which improves overall performance.
5.1.3 Load PSA DB2 compression
Because character strings are often repeated in the PSA table, DB2
compression usually improves the load performance. The repeated strings allow
a high degree of compression for the data in the PSA table. In SAP BI, the
tablespaces for PSA tables are created with the COMPRESS YES option and
the DB2 data compression is activated. Compression leads to less I/O and
improved utilization of the bufferpool which, in turn, enhances overall
performance.
Compression can be turned off by setting DB2_PSA_COMPRESS = NO in the
table RSADMIN, but this should be done on an exception basis.
Chapter 5. Best practices for PSA 69