DB2 UDB for z/OS Version 8 Performance Topics - IBM Redbooks

16 EB
2 GB
64-bit summary
64-bit AS
31-bit AS
Figure 2-1 Virtual storage growth
DB2 code
2.5.2 No more hiperpools and data spaces
Buffer pool
RID pool
Sort pool
BP ctl blks
Compr dict
Castout buf
DBD, DSC
DB2 code
Locks
IRLM code
DB2 code
User pgm/st proc MSTR DBM1 IRLM DDF
In DB2 V8 CM, there are no longer hiperpools and buffer pools in data spaces; if they existed
prior to the migration, they automatically revert to buffer pools. DB2 automatically reallocates
the buffer pool sizes based on the original virtual buffer pools and the hiperpools or buffer
pools in data spaces. For example, if BP4 consisted of 4,000 virtual buffer pool pages and
20,000 hiperpool pages, then after the migration, BP4 contains 24,000 pages in a buffer pool.
These buffer pools are automatically allocated and reside above the 2 GB bar. DB2 no longer
uses the terminology virtual pool and instead uses buffer pool. The total buffer pool storage
must never exceed the real storage available for buffers. There are also reasonableness
checks for 1 terabyte of storage for a single buffer pool and for the sum of all buffer pools. Not
only do the buffer pools reside above the bar, but so do the corresponding buffer pool control
blocks.
Important: If you are using a large number of hiper pools with V7, review the buffer pool
definitions before your DB2 V8 migration. Make sure you have adequate real storage, and
also adjust the thresholds of the new buffer pools, especially if they are not defined in
percentages. When in doubt, use the V8 defaults.
An important performance consideration here is to make sure you have enough real storage
to back these entities. If you do not, you can encounter severe performance penalties for
paging; since expanded storage no longer exists, you page to DASD.
One immediate benefit of having one type of buffer pool is simplification, and you also have
immediate virtual storage constraint relief. This factor alone can move you toward increasing
the number of threads, but since the thread-related storage stays below the bar, we do not
recommend this type of change so soon after migrating to CM without verification.
Chapter 2. Performance overview 19