1. Memory Management in DB2 10
for z/OS
Julian Stuhler
Principal Consultant
Triton Consulting
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2. Acknowledgements
• John Campbell
• Michael Dewert
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3. Agenda
• Introduction
• What’s Changed & Why?
• What Does It Mean for Me?
• Summary & Questions
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4. Introduction
• Julian Stuhler
 Director and Principal Consultant at Triton Consulting
 24 years DB2 experience, 19 as a consultant working with
customers in UK, Europe and the US
 IBM Gold Consultant since 1999
 IBM Information Champion
 Former IDUG (International DB2 User Group) President
 Author of IBM Redbooks, white papers and more recently
“flashbooks”
 Designer of IBM’s new “DB2 10 Business Value Assessment
Estimator Tool”
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5. What’s Changed and Why?
The Need for Scalability
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6. 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
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7. 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)
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8. Virtual Storage Enhancements
Castout buffers Castout buffers Castout buffers
Compression Dict Compression Dict Compression Dict
DBD Cache DBD Cache DBD Cache
Global DSC Global DSC Global DSC
RIDPOOL RIDPOOL RIDPOOL
SORTPOOL SORTPOOL SORTPOOL
SKCT + PT SKCT + PT
CT + PT
Thread
EDMPool CT + PT (Pointers)
All storage Thread Storage Thread Storage Dataset Storage
Dataset Storage Dataset Storage
V7 V8 V9 V10
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9. Real Storage Enhancements
• For prior releases, z/OS DB2 9 Buffer Pool
always managed DB2
bufferpool pages as 4K
frames
z/OS Storage
• Move to 64-bit architecture
made much larger buffer
pools viable
 Bufferpools can use many
millions of pages 4K
 Increased z/OS overheads Pages
for page management 4K
Pages
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10. Real Storage Enhancements
• DB2 10 introduces support for
1MB pages to reduce z/OS page
management overheads DB2 10 Buffer Pool
 Needs z10 or newer z196 server
 Needs bufferpool to be defined
with PGFIX=YES
z/OS Storage
 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 4K
reduction Pages
 Customer testing during beta
program showed CPU reductions 1MB
of 0-6% with this feature enabled Pages
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11. What Does It Mean For Me?
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12. Real Storage Availability
• 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
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13. 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 will be around 75% less than for a z10
• 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
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14. 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 APAR
OA37821 and corresponding DB2 APAR PM49816 are also applied – see later
 Both APARs marked as HIPER – you are strongly advised to implement the associated PTFs
before migrating to DB2 10 in any production environments!
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15. 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
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16. 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
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17. 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
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18. 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
 Needs IPL to implement z/OS fix
• 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
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19. 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)
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20. 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 VSCR enhancements are available in CM,
but you need package rebind to get maximum benefits
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21. 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
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22. 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
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23. 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!
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24. Summary & Questions
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25. 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
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26. Feedback / Questions
Julian Stuhler – julian.stuhler@triton.co.uk
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27. Additional Information
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28. 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
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29. 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
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30. 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/
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