DB2 10 for z/OS includes major enhancements to memory management that allow most DB2 storage objects to reside above the 2GB bar, providing up to a 10x increase in threads per subsystem. This reduces a key scalability limitation. To take advantage of these virtual storage improvements, additional real memory is required, typically a 10-30% increase over DB2 9 requirements. Customers should also monitor and manage real storage usage with new DB2 10 functions to avoid paging issues. The virtual storage changes along with other DB2 10 capabilities could allow for reduced DB2 subsystem counts and improved performance.

1. The Information Management Specialists
Memory Management in
DB2 10 for z/OS
Julian Stuhler
UK DB2 GUIDE Meeting, June 2013

2. The Information Management Specialists
Acknowledgements
• John Campbell
• Michael Dewert
• James Gill

3. The Information Management Specialists
Agenda
• Introduction
• What’s Changed & Why?
• What Does It Mean for Me?
• Summary & Questions
Win a limited edition 30th
Anniversary DB2 Geek T-Shirt
for asking me a question!

4. The Information Management Specialists
Introduction
• Julian Stuhler
 Director and Principal Consultant at Triton
Consulting
 25 years DB2 experience, 20 as a consultant working with
customers in UK, Europe and the US
 IBM Gold Consultant since 1999
 IBM Information Champion
 IDUG Past President
 Author of IBM Redbooks, white papers and more recently
“flashbooks”
 Designer of IBM’s DB2 10 Business Value Assessment Estimator
Tool

5. The Information Management Specialists
What’s Changed and Why?
The Need for Scalability

6. The Information Management Specialists
The Need for Scalability
• IT volumes continue to increase
 More applications
 More data
 More transactions
• Performance is ever more important
 Customers need to support workload growth without a drop-off in
performance
• Availability is ever more important
 Pressure to reduce both planned and unplanned outages
• End result: each DB2 environment is being asked to work harder, with less
downtime
• Every DB2 release attempts to push back these boundaries, but major
progress has been made in DB2 10

7. The Information Management Specialists
DB2 Storage Usage – DBM1 storage
below the bar
0 231
(2GB)
232
(4GB)
“The Bar”
224
(16MB)
“The Line”
Typically 800 – 1900 MB
Available to DB2
Typically 7 – 9 MB
Available to DB2

8. The Information Management Specialists
Virtual Storage Enhancements
• V8 began a major project to
transform DB2 into a 64-bit RDBMS
 Laid the groundwork and provided
some scalability improvements but a
lot of DBM1 objects remained below
the 2GB bar
• DB2 9 improved things a little, but
only by another 10-15% for most
customers
 Practical limit of 300-500 threads per
DB2 subsystem
• DB2 10 moves 80-90% of the
remaining objects above the
bar, resulting in 5-10x improvement
in threads per subsystem (CM)

9. The Information Management Specialists
Virtual Storage Enhancements
All storage
EDMPool
Thread Storage
Dataset Storage
Castout buffers
Compression Dict
DBD Cache
Global DSC
RIDPOOL
SORTPOOL
CT + PT
Thread Storage
Dataset Storage
Castout buffers
Compression Dict
DBD Cache
Global DSC
RIDPOOL
SORTPOOL
SKCT + PT
(Pointers)
Dataset Storage
Castout buffers
Compression Dict
DBD Cache
Global DSC
RIDPOOL
SORTPOOL
SKCT + PT
CT + PT
Thread
V7 V8 V9 V10

10. The Information Management Specialists
Real Storage Enhancements
• For prior releases, z/OS
always managed DB2
bufferpool pages as 4K
frames
• Move to 64-bit architecture
made much larger buffer
pools viable
 Bufferpools can use many
millions of pages
 Increased z/OS overheads
for page management
DB2 9 Buffer Pool
z/OS Storage
4K
Pages
4K
Pages

11. The Information Management Specialists
Real Storage Enhancements
• DB2 10 introduces support for 1MB
pages to reduce z/OS page
management overheads
 Needs z10/z196/zEC12 server
 Needs bufferpool to be defined
with PGFIX=YES
 z/OS sysprogs must partition real
storage between 4K and 1MB
frames (IESYSnn in PARMLIB, needs
IPL) so wait until DB2 10 is bedded
in
• Key part of potential DB2 10 CPU
reduction
 Customer testing during beta
program showed CPU reductions of
0-6% with this feature enabled
DB2 10 Buffer Pool
z/OS Storage
4K
Pages
1MB
Pages

12. The Information Management Specialists
What Does It Mean For Me?

13. The Information Management Specialists
Real Storage Availability
• DB2 10 removes most virtual storage
constraints, but you need sufficient
real storage to back any increased
virtual storage usage
 Paging will still kill you in a 64-bit
environment, should be near zero
• Plan on additional 10-30% real memory for DB2 following
migration from DB2 9
 Most customers will be at lower end of this range, but more will
be required once you start using some DB2 10 capabilities.
 Skip migration customers will need more

14. The Information Management Specialists
Real Storage Availability
• Insufficient real storage to back usage of virtual leads to paging activity
• It is critical to ensure that page-in activity (aka “demand paging”) for DB2
address spaces is minimised (near zero)
 No expanded storage in 64-bit environment, all paging is to disk (AUX)
 Any page-in operation is very expensive in performance terms compared to
page hit in real storage
 Note that page-out operations are normal for rarely-used pages and not
usually a cause for concern
• Real storage shortages can have serious impact on stability of overall
system
 If all AUX is consumed, LPAR goes into wait state and may fail
 Can lead to long system dump processing times, with high risk of system-wide
slowdowns and incomplete dumps

15. The Information Management Specialists
Real Storage Availability
• You also need to allow approx. 16GB for DB2 dump requirement (twice the
8GB value recommended for DB2 8 and 9)
 MAXSPACE parameter defines max amount of virtual storage for SVC dump –
z/OS default is 500MB
 Some customer horror stories due to insufficient storage being available for
dumps
• Good news if you’re on a z196, as the “technology dividend” means that
cost per GB is around 75% less than for a z10
 Cheaper still for zEC12
• Many customers are already running lean on real storage even under V9,
and are building real storage increase costs into their DB2 10 financial
justifications

16. The Information Management Specialists
Real Storage Monitoring
• Statistics IFCID 225 has long been vital for DB2 storage monitoring
 Part of Statistics Class 1 trace since PQ99658, so now enabled by default
• Once DB2 10 is implemented in your environment, focus should change
from virtual to real storage monitoring
• PM24723 and PM37647 introduce important real storage monitoring and
contraction enhancements
 ICFID 225 enhanced with new fields to externalise real and auxiliary storage
consumption for storage objects in private, shared, and common areas above
the bar (see additional information at end of presentation)
 Introduces two new DSNZPARMs to tell DB2 if and how to release any unused
real storage (REALSTORAGE_MANAGEMENT) and specify upper limit on DB2
real storage usage (REALSTORAGE_MAX) – see next slide
 Some increase in MSTR CPU due to storage monitoring. Make sure PTFs for
z/OS APAR OA37821 and corresponding DB2 APAR PM49816 are also applied –
see later

17. The Information Management Specialists
Real Storage Monitoring
• Opaque DSNZPARMs introduced by PM24723 and PM37647
• REALSTORAGE_MANAGEMENT
 ON – Unused backed real frames discarded when possible (CPU overhead)
 OFF – DB2 will only discard unused frames when critical real storage or auxiliary storage usage
is detected
 AUTO (default) – DB2 will discard unused frames when the system begins to page
 Recommended value = AUTO
 DSNV516I and DSNV517I written when DB2 enters and exits real storage contraction mode
• REALSTORAGE_MAX
 Hard limit on real and auxiliary storage used by DB2 subsystem – DB2 will terminate if limit
reached
 Valid values: NOLIMIT (default), 1 – 65,535 (GB)
 Recommended value = 2 x amount of real and auxiliary storage that the subsystem might
reasonably consume
 DSNS003I written when DB2 approaches the threshold and DSNS004I written to indicate relief
from this condition

18. The Information Management Specialists
Real Storage – Other Issues
• Ensure PTFs for z/OS APAR APAR OA37821 and corresponding DB2 APAR PM49816
are applied
 Fixes MSTR CPU issue associated with MVS COUNTPAGES function used for real storage
monitoring (introduced by our good friend PM24723)
 Especially noticable where more than one DB2 subsystem resides on same LPAR,or on an idle
system
 Needs IPL to implement z/OS fix
 Both APARs marked as HIPER – you are strongly advised to implement the associated PTFs
before migrating to DB2 10 in any production environments
• What about CONTSTOR and MINSTOR?
 Enabling these ZPARMs in previous releases allowed you to spend a little more CPU in
exchange for improved virtual storage utilisation
 Both ZPARMs apply to 31-bit storage only, so are less important in DB2 10
 Recommendation is CONTSTOR=MINSTOR=NO once you have proven VSCR in DB2 10

19. The Information Management Specialists
Other Limiting Factors
• DBM1 Virtual Storage should no longer be an issue, but
other limiting factors on vertical scalability still remain
 ESQA/ECSA (31-bit) storage
 Active log write contention (LC19)
 SMF volumes (DB2 10 SMF compression can help)

20. The Information Management Specialists
Use New DB2 10 Features
• Only consider use of new features when you are sure
you have fully considered all the previous items and
DB2 10 is properly “bedded in”
• Remember that some VSCR enhancements are
available in CM, but you need package rebind to get
maximum benefits

21. The Information Management Specialists
Use New DB2 10 Features
• Exploit 1MB real storage frames
 Needs PGFIX=YES, but many customers still haven’t exploited
this feature in their DB2 8 and DB2 9 systems despite significant
potential CPU savings (up to 6% seen)
 PGFIX=YES benefits dependent on I/O rate, and you need to
back pools 100% with real storage (scary if you’re already
running lean on real storage availability)
 1MB page frames specified by LFAREA in IEASYSnn parmlib
member, and need IPL to implement
► Use /DISPLAY VIRTSTOR,LFAREA after implementation to ensure sizing
is OK, as conversion between 4K and 1MB frames costs CPU
 Ensure you are up to date on z/OS maintenance before enabling

22. The Information Management Specialists
DB2 10 Real Storage Enhancements
• 1MB page frame support for buffer pools
 CPU savings of up to 4% by reducing z/OS
page management overheads for big BPs
► DB2 BPs can be up to 1TB total in DB2 9 and
10, with limit of 2x available real storage
 z/OS sysprogs must partition real storage
between 4K and 1MB frames
► LFAREA parm in IEASYSnn PARMLIB
(expressed in %, MB or GB, 80% max)
► Need IPL to change LFAREA, so ensure DB2 10
is properly “bedded in” before implementing!

23. The Information Management Specialists
DB2 10 Real Storage Enhancements
• z/OS can decompose 1MB pages into 256 x 4KB pages, or recombine 4KB pages
into 1MB pages if SOS condition occurs
 Costs CPU and elapsed time so should be avoided by setting LFAREA appropriately
LFAREA
Decompose / recombine

24. The Information Management Specialists
Tuning – Setting LFAREA
• Sizing guideline
 Review BPs and set PGFIX=YES where suitable
► Ensure sufficient real storage to back BP
► See BP tuning section earlier
 Set LFAREA = SUM (page-fixed BPs) + 10%
► Assumes DB2 is only major user of 1MB page frames, but allows 10% “wriggle
room”
 Verify sizing is correct (after IPL and DB2 BP allocation!)
► /DISPLAY VIRTSTOR,LFAREA (no decomposition)
► -DIS BUFFERPOOL(nn) SERVICE=4 (no 4K pages used for page-fixed buffer
pools)
• Review LFAREA whenever BP sizes, page-fix attribute etc is changed
 Sysprogs and DBAs must co-ordinate activities (should be BAU!)

25. The Information Management Specialists
Real Storage Monitoring
• Monitor use of 1MB page frames used by a specific BP
 -DISPLAY BUFFERPOOL(BPnn) SERVICE=4
 Resultant DSNB999I message shows number of 1MB pages in use
-DBA1 DIS BUFFERPOOL(BP0) SERVICE=4
DSNB401I -DBA1 BUFFERPOOL NAME BP0, BUFFERPOOL ID 0, USE COUNT 246
DSNB402I -DBA1 BUFFER POOL SIZE = 5000 BUFFERS AUTOSIZE = NO 641
ALLOCATED = 5000 TO BE DELETED = 0
IN-USE/UPDATED = 172
DSNB406I -DBA1 PGFIX ATTRIBUTE - 642
CURRENT = NO
PENDING = NO
PAGE STEALING METHOD = LRU
DSNB404I -DBA1 THRESHOLDS - 643
VP SEQUENTIAL = 80
DEFERRED WRITE = 30 VERTICAL DEFERRED WRT = 5, 0
PARALLEL SEQUENTIAL =50 ASSISTING PARALLEL SEQT= 0
DSNB999I -DBA1 DSNB1DBP SERVICE( 4 )OUTPUT
DSNB999I -DBA1 4K PAGES 5000
DSNB999I -DBA1 1M PAGES 0
DSN9022I -DBA1 DSNB1CMD '-DIS BUFFERPOOL' NORMAL COMPLETION

26. The Information Management Specialists
Real Storage Monitoring
• Monitor use of 1MB page frames across LPAR
 /DISPLAY VIRTSTOR,LFAREA (needs APAR OA31116)
 IAR019I message shows breakdown of 4KB and 1MB page frames and
how much of each is currently available
 HWM usage is also shown – useful for ensuring correct segmentation
of 4K and 1MB pages in z/OS
/DISPLAY VIRTSTOR,LFAREA
IAR019I 12.31.04 DISPLAY VIRTSTOR
SOURCE = GS
TOTAL LFAREA = 1024M
LFAREA AVAILABLE = 1023M
LFAREA ALLOCATED (1M) = 10M
LFAREA ALLOCATED (4K) = 2M
MAX LFAREA ALLOCATED (1M) = 10M
MAX LFAREA ALLOCATED (4K) = 2M
Current / HWM LFAREA
allocated for 4KB pages
(pages decomposed)

27. The Information Management Specialists
Use New DB2 10 Features
• Possibility for less DB2
subsystems (and possibly
less LPARs) in a data sharing
environment
 Lower data sharing overhead
 Less systems to manage /
maintain
 Minimum of 4 members / 2
LPARs still recommended for
high availability

28. The Information Management Specialists
Use New DB2 10 Features
• More space for performance critical storage objects such as dynamic
statement cache
 Improve DSC hit ratio and reduce CPU accordingly
 Potential for significant MAXKEEPD increase is a key part of the overall DB2 10
value proposition for SAP customers
• Potential to reduce CPU cost through more use of persistent threads with
RELEASE(DEALLOCATE)
 CICS protected entry threads
 DB2 10 High-Performance DBATs
 Remember trade-off on BIND/DDL concurrency with use of
RELEASE(DEALLOCATE)
• Don’t forget that you’ll need to allocate additional real storage to back any
increases above!

29. The Information Management Specialists
The Future
• IBM announced zEnterprise EC12 in August 2012
 12th generation processor, running at 5.5GHz
 Up to 101 configurable processors per server
 Flash express – up to 6.4TB of SSD as a new
memory tier between RAIM and disk
• Several new memory-related features planned
 DB2 code backed by 1MB page frames
 Pageable 1MB page frames (no need for PGFIX=YES)
 Support for (non pageable) 2GB page frames
 Support for Flash express
• IBM statement of direction for DB2 exploitation of these features in a
future release 

30. The Information Management Specialists
Summary & Questions

31. The Information Management Specialists
Summary
• Make sure you have enough real storage before upgrading to DB2
10
• Change your focus from monitoring virtual storage to monitoring
real storage
• If you are scaling vertically or consolidating subsystems, be aware of
other limiting factors that were previously invisible but may now
come to bite you
• Once you’ve addressed ALL of the above, start to make use of the
new DB2 10 storage-related features
 Remember to add more real storage as required in order to prevent
paging

32. The Information Management Specialists
Feedback / Questions
Julian Stuhler – julian.stuhler@triton.co.uk
Triton Consulting
25 Bank Plain
Norwich NR2 4SF
www.triton.co.uk

33. The Information Management Specialists
Additional Information

34. The Information Management Specialists
Real Storage Monitoring – New IFCID
225 Counters
ADDRESS SPACE SUMMARY – DBM1
EXTENDED REGION SIZE (MAX) : 1587544064 24-BIT LOW PRIVATE : 221184
24-BIT HIGH PRIVATE : 450560 31-BIT EXTENDED LOW PRIVATE : 69603328
31-BIT EXTENDED HIGH PRIVATE : 38600704 CURR HIGH ADDR 24-BIT PRIV REGION : X’0003C000’
CURR HIGH ADDR 31-BIT PRIV REGION : X’270E9000’ 31-BIT RESERVED FOR MUST COMPLETE : 158754406
31-BIT RESERVED FOR MVS : 25827760 STORAGE CUSHION WARNING TO CONTRACT: 158754406
TOTAL 31-BIT GETMAINED STACK : 4341760 TOTAL 31-BIT STACK IN USE : 3997696
TOTAL 31-BIT VARIABLE POOL : 12836864 TOTAL 31-BIT FIXED POOL : 86016
TOTAL 31-BIT GETMAINED : 1002384 AMOUNT OF AVAILABLE 31-BIT : 1479335936
SYSTEM AGENT STACK STORAGE IN USE : 1234567
TOTAL 64-BIT VARIABLE POOL : 10162176 TOTAL 64-BIT FIXED : 7503872
TOTAL 64-BIT GETMAINED : 438127168 TOTAL 64-BIT PRIVATE FOR STOR MANAG: 1925120
REAL 4K FRAMES IN USE : 20577 AUXILIARY SLOTS IN USE : 41227
64-BIT REAL 4K FRAMES IN USE : 12129 64-BIT 4K AUX SLOTS IN USE : 27055
ABOVE VALUE W/O BP STORAGE : 10000 ABOVE VALUE W/O BP STORAGE : 4096
HWM 64-BIT REAL 4K FRAMES IN USE : 43047 HWM 64-BIT AUX SLOTS IN USE : 27059
QW0225CTLP (S) : OFF QW0225CTLS (S) : OFF

35. The Information Management Specialists
Real Storage Monitoring – New IFCID
225 Counters
SHARED/COMMON STORAGE SUMMARY
EXTENDED CSA SIZE : 315179008 31-BIT COMMON FIXED POOL : 1122304
31-BIT COMMON VARIABLE POOL : 716800 31-BIT COMMON GETMAINED : 79661
64-BIT COMMON FIXED POOL : 3641344 64-BIT COMMON VARIABLE POOL : 37748736
64-BIT COMMON GETMAINED : 0 64-BIT COMMON FOR STOR MANAG : 1400832
64-BIT SHARED VARIABLE POOL : 13545472 64-BIT SHARED FIXED : 3129344
64-BIT SHARED GETMAINED : 4220208 64-BIT SHARED FOR STOR MANAG : 2056192
64-BIT SHR SYSTEM AGENT STACK (AS) : 268435456 64-BIT SHR SYSTEM AS IN USE : 33554432
64-BIT SHR NON-SYSTEM AS : 805306368 64-BIT SHR NON-SYSTEM AS IN USE : 1048576
SHARED MEMORY OBJECTS : 5
64-BIT SHARED MEMORY PAGES : 117440512 HWM 64-BIT SHARED BYTES : 481036337152
64-BIT SHARED PAGES BACKED IN REAL : 9395 AUX SLOTS USED FOR 64-BIT SHARED : 5385
64-BIT PAGES PAGED IN FROM AUX STO : 5317 64-BIT PAGES PAGED OUT TO AUX STO : 41577
64-BIT SHR STG REAL 4K FRMS IN USE : 12344459 64-BIT SHR STG 4K AUX SLTS IN USE : 512
64-BIT STK STG REAL 4K FRMS IN USE : 12345789 64-BIT STK STG 4K AUX SLTS IN USE : 256
64-BIT COM STG REAL 4K FRMS IN USE : 12345123456789 64-BIT COM STG 4K AUX SLTS IN USE : 1234555555
SERVICE INFORMATION:
QW0225_WARN : 0 QW0225_REALAVAIL : 0
QW0225_REALAVAILLO : 0 QW0225_REALAVAILOK : 0
QW0225_ESQAS : 0 QW0225_ESQA_ALLOC : 0
QW0225_ESQA_HWM : 0 QW0225_ECSA_ALLOC : 0
QW0225_ECSA_HWM : 0 QW0225_ECSA_CONV : 0
QW0225_CTGP : OFF QW0225_DISC : OFF

36. The Information Management Specialists
Further Reading
• IBM DB2 10 Home Page
 http://www-01.ibm.com/software/data/db2/zos/db2-10/
• White Paper – DB2 10: A Smarter Database for a Smarter Planet
 https://www14.software.ibm.com/webapp/iwm/web/signup.do?source=s
w-infomgt&S_PKG=wp-z-db2-smarter
 Also available as part of a “flashbook” - ISBN: 1583473610
• DB2 10 for z/OS Performance Topics Redbook (SG24-7942)
 http://www.redbooks.ibm.com/abstracts/sg247942.html?Open
• IDUG – International DB2 User Group
 http://www.idug.org/