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

► Reduced the number of objects using compression to minimize the number of
compression dictionaries
2.3.1 DB2 structures above the bar
In DB2 V8 the data space buffer pool, data space lookaside pool, and hiper pools have been
eliminated. Many elements have moved above the 2 GB bar, including the virtual buffer pools
and their control blocks. Here are some areas now located above the 2 GB bar:
► Buffer pools
► Buffer pool control blocks
► Compression dictionaries
► EDM pool components for DBDs and dynamic statement cache
► Sort pool
► RID lists
What does this mean for the application? You need to examine the extra storage gained and
decide what to do with it. The application may improve with larger buffer pools and since
these reside above the 2 GB bar, it may be the vehicle that reduces execution time to the
application. Or you may decide to enlarge the EDM pool or Sort pool.
If you were using the DSNZPARM CONTSTOR and MINSTOR to contract thread storage,
and thread storage is not critical, you can now consider turning this off, eliminating the CPU
overhead usage attributed to storage contraction.
If you are a heavy user of compression, you benefit from making more storage available
below the bar.
2.3.2 What are the implications of more storage?
2.4 Real storage
Are you able to expand the number of active threads? It depends on the storage footprint for
threads. How many additional threads can be supported varies by workload and depends on
various factors such as:
► Duration of the thread
► SQL workload
► BIND parameters RELEASE
If you have already exploited the virtual storage constraint relief recommendations above, the
added benefit when you migrate to DB2 V8 can possibly result in additional virtual storage
relief. If you have not done anything, the added benefit should be higher. To summarize, this
added virtual storage relief can help customers currently experiencing virtual storage
constraint problems in DB2 V7. But, if you are currently monitoring storage closely, then plan
to continue monitoring in V8.
If IRLM is a significant consumer of ECSA, you can consider decreasing ECSA, since the
IRLM no longer has its locks in ECSA.
A key message is you must have the real storage to fully back increased storage use;
otherwise, you risk paging that adversely affects performance. Remember that expanded
storage no longer exists in this environment, and therefore, any paging goes directly to disk;
the effect can be immediately significant.
Chapter 2. Performance overview 17