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

your buffer pools. We recommend you implement long term page fixing, buffer pool by
buffer pool, for I/O intensive profiles. See 4.5, “Buffer pool long term page fixing” on
page 169, for a more detailed discussion on long term page fixing.
► Multi-row FETCH and INSERT
Although this DB2 V8 enhancement requires you to modify your application, it has a
significant potential to save CPU cycles. See the sections on Multi-row FETCH and
INSERT in Chapter 3, “SQL performance” on page 29 for more details.
4.2 Virtual storage constraint relief
DB2 V8 exploits 64-bit storage in the DBM1 address space which provides significant virtual
storage constraint relief (VSCR).
By way of background, MVS addressing is represented in the power of 2 closest to the
corresponding power of 10. Refer to the z/Architecture Principles of Operation, SA22-7832 for
a more detailed discussion.
2#10 Kilo (1024 bytes)
2#20 Mega (1024 * 1024 bytes)
2#30 Giga (1024 * 1024 * 1024 bytes)
2#40 Tera (1024 * 1024 * 1024 * 1024 bytes)
2#50 Peta (a really big number)
2#60 Exa (an even bigger number)
2#70 Zetta (too big a number)
2#70 Yotta (the “Restaurant at the end of the Universe!”)
So 2#64 is 16EB -- and the largest z/Architecture address is 16E-1. DB2 now supports a
16-exabyte DBM1 address space. A 16-exabyte address space is 8 billion times larger than a
2-gigabyte (GB) address space. The new virtual storage area above the old 2 GB limit is
referred to as above the bar.
Figure 4-3 provides a simplified introductory description of the major storage areas that have
moved above the 2 GB bar in the DBM1 address space. The 64-bit storage exploitation in
DB2 V8 provides a number of performance improvements to DB2 which we discuss in this
section.
The entities which have been moved above the bar in the DB2 V8 DBM1 address space
include:
► 64-bit virtual buffer pool and their control blocks
Larger buffer pools enable I/O reduction for random access, and enable larger page sizes
which benefit sequential access. Buffer pool management is also made simpler.
► DBDs in the EDM pool
More database objects can be defined and I/O to the DB2 directory is reduced because
the pool can be larger.
► EDM statement cache
A larger cache may avoid dynamic SQL PREPAREs.
► Compression dictionaries
You no longer need to manage the open and close for table spaces to manage the amount
of DBM1 storage which is required by compression dictionaries for open compressed table
spaces.
► Sort pools
Chapter 4. DB2 subsystem performance 139