zIIP Capacity Planning - May 2018
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This document provides a summary of an IBM presentation on zIIP Capacity Planning. The presentation covered: 1) The importance of zIIP Capacity Planning given recent software enhancements that increase zIIP eligibility 2) Recent DB2 versions have significantly increased the amount of work eligible to run on zIIPs, including critical address spaces 3) Proper zIIP Capacity Planning requires measuring potential and actual zIIP usage at the address space level using tools like RMF
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zIIP Capacity Planning - May 2018
- 1. 2018 IBM Systems Technical University May 2018 London zIIP Capacity Planning — Martin Packer IBM
- 2. Please note • IBM’s statements regarding its plans, directions, and intent are subject to change or withdrawal without notice and at IBM’s sole discretion. • Information regarding potential future products is intended to outline our general product direction and it should not be relied on in making a purchasing decision. • The information mentioned regarding potential future products is not a commitment, promise, or legal obligation to deliver any material, code or functionality. Information about potential future products may not be incorporated into any contract. • The development, release, and timing of any future features or functionality described for our products remains at our sole discretion. • Performance is based on measurements and projections using standard IBM benchmarks in a controlled environment. The actual throughput or performance that any user will experience will vary depending upon many factors, including considerations such as the amount of multiprogramming in the user’s job stream, the I/O configuration, the storage configuration, and the workload processed. Therefore, no assurance can be given that an individual user will achieve results similar to those stated here. 2
- 3. zIIP Capacity Planning Martin Packer, IBM [email protected] Twitter/Facebook: martinpacker 1
- 4. Abstract zIIP Capacity Planning tends to be neglected - in favour of General-Purpose Engines (GCPs). With recent enhancements to DB2 allowing you to offload critical CPU to zIIPs, and to get the most out of zAAP-on-zIIP, it's time to take zIIP Capacity Planning seriously. This presentation describes how to do zIIP Capacity Planning properly - with instrumentation and guidelines. Note: Updated for z13 SMT and numerous exploiting software updates 2
- 5. Topics If You Only Remember 4 Things The Importance Of zIIP Capacity Planning Recentish News DB2 Criticality So Let's Take This Seriously... Miscellaneous Topics Conclusion Appendix - DB2 Address Spaces (Thanks To John Campbell) 3
- 6. If You Only Remember 4 Things The Importance Of zIIP Capacity Planning Recentish News DB2 Criticality So Let's Take This Seriously... Miscellaneous Topics Conclusion Appendix - DB2 Address Spaces (Thanks To John Campbell) 4
- 7. If You Only Remember 4 Things • Capacity Planning for zIIPs has become much more important • Pay especial attention to what % Busy represents “full” • Measure zIIP potential and usage down to the address space level • Consider LPAR configuration carefully for zIIPs 5
- 8. If You Only Remember 4 Things The Importance Of zIIP Capacity Planning Recentish News DB2 Criticality So Let's Take This Seriously... Miscellaneous Topics Conclusion Appendix - DB2 Address Spaces (Thanks To John Campbell) 6
- 9. Why People Don't Do zIIP Capacity Planning • zIIPs are much cheaper than general purpose processors (GCPs) • Maintenance cost lower also • zIIPs don't attract a software bill • zIIP Utilization hasn't historically been all that high • zIIP-eligible work can spill to GCPs at a pinch • zIIPs are sometimes not the most carefully considered part of a purchase • Ignoring zIIPs, ICFs, IFLs, zAAPs simplifies things to a single processor pool 7
- 10. But Consider • Spilling to a GCP costs money • Not spilling to a GCP can cost performance & scalability • zIIPs aren't free • Shoving another processor book in can be difficult or impossible • And at end of processor life upgrades become impossible • More software that exploits zIIP installed • Some more performance-critical than previous exploiters • New and modernised applications increasingly use zIIP • LPAR configuration for zIIPs affects their performance 8
- 11. If You Only Remember 4 Things The Importance Of zIIP Capacity Planning Recentish News DB2 Criticality So Let's Take This Seriously... Miscellaneous Topics Conclusion Appendix - DB2 Address Spaces (Thanks To John Campbell) 9
- 12. Recent (& Now Not-So-Recent) News • zAAP On zIIP • Even with zAAPs installed • zAAP gone with z14 • New 2:1 zIIP:GCP configuration rule with z13, zEC12 and zBC12 processors • DB2 Version 10 Deferred Write and Prefetch Engines • DB2 Version 11 further exploiters • DB2 Version 12 yet more exploiters • z13 zIIP SMT • z/OS HonorPriority at Service Class Level (OA50845 / OA50953) • z/OSMF Autostart in z/OS 2.3 • Java but Liberty Profile 10
- 13. If You Only Remember 4 Things The Importance Of zIIP Capacity Planning Recentish News DB2 Criticality So Let's Take This Seriously... Miscellaneous Topics Conclusion Appendix - DB2 Address Spaces (Thanks To John Campbell) 11
- 14. DB2 Version 10 Deferred Write And Prefetch Engines • Substantial portion of DBM1 address space CPU • Changed by APAR PM30468 from MSTR address space • 100% eligible for zIIP • Very stringent performance requirements • Must not be delayed • Latency to cross over to GCP generally too high • Substantially changes zIIP Capacity Planning rules • Treat DBM1 as a key address space and protect its access to CPU, including zIIP 12
- 15. 13
- 16. DB2 Version 11 Exploits zIIP Still Further • Clean up of pseudo deleted index entries as part of DB2 system task cleanup • Clean up of XML multi-version • Log write and log read • Clean up of pseudo deleted index entries • Portions of XML multi version documents cleanup • System related asynchronous SRB processing with the exception of P-lock negotiation processing. • MSTR System related asynchronous SRB processing, such as log write or log read • More Utilities eligibility 14
- 17. DB2 Version 12 Even More zIIP Exploitation • Parallel child tasks of an SQL query can now be 100% zIIP eligible • Previously only 80% • REORG: Reload phase is now 100% zIIP eligible • ~up to 17% more for REORG • LOAD: Reload phase is now 100% zIIP eligible • ~up to 90% more for LOAD • PI73882 initial Non-Parallel implementation • PI80243 added Parallel • Automatic GRECP/LPL recovery retry is 100% zIIP eligible • Task which checks every 2 minutes whether an index is an FTB candidate • Fast Traverse Blocks (FTBs) are in-memory structures for non-leaf index pages 15
- 18. If You Only Remember 4 Things The Importance Of zIIP Capacity Planning Recentish News DB2 Criticality So Let's Take This Seriously... Miscellaneous Topics Conclusion Appendix - DB2 Address Spaces (Thanks To John Campbell) 16
- 19. Many Sources Of Information • From RMF: • SMF 70 • SMF 72-3 • From z/OS: • SMF 30 • From middleware: • SMF 101 DB2 Accounting Trace • SMF 110 CICS Statistics Trace • NOTE: SMT adds considerable metrics complexity 17
- 20. From 70-1: 18
- 21. 19
- 22. From 72-3: (Slide is for zIIP on GCP) 20
- 24. Service Class (Period) Information • For Velocity Goal service class periods you get samples... • For work that's not zIIP eligible you get e.g. Using and Delay samples for CPU and I/O • These are the sample counters that affect the velocity calculation • With zIIP-eligible work you get better resolution – as you get Using and Delay samples specific to zIIP • Useful to correlate Delay for zIIP with % zIIP on GCP • Can explain behaviour 22
- 25. A Sample DDF-Related Service Class 23
- 26. Understanding Your Exploiters • Exploiters come in different shapes and sizes • And leave “footprints” accordingly • Likewise different criticality levels • Which ought to be reflected in WLM setup • Dependent Enclave • e.g. DBM1 Prefetch / Deferred Write • Independent Enclave • e.g. DDF • zAAP-on-zIIP • Formerly zAAP-eligible e.g. Java • e.g. Dependent Enclave for DBM1 Address Space is Performance Critical from DB2 Version 10 24
- 27. SMF 30 Shift-Level Summary Of zIIP Exploiters 25
- 28. A DB2 Version 10 DBM1 Address Space's zIIP and CPU Usage Over 24 Hours 26
- 29. Projections • Projecting Near-Term zIIP CPU Requirements: • For existing workloads that don't run on a zIIP: • “Project CPU” reports how much CPU is zIIP-eligible via RMF • DB2 V10 to V11 or later: • The remainder becoming zIIP-eligible is a reasonable estimate • Probably about 20% • None of it any less “stringent” • For workloads that don't exist yet use any sizing guidelines you can get • Some “adaptive exploiters” exist: • These only try to use zIIP if one configured • “Project CPU” will show zero • Projecting Into The Future • The same as standard CPU Capacity Planning 27
- 30. If You Only Remember 4 Things The Importance Of zIIP Capacity Planning Recentish News DB2 Criticality So Let's Take This Seriously... Miscellaneous Topics Conclusion Appendix - DB2 Address Spaces (Thanks To John Campbell) 28
- 31. zIIP “Short Engine” Effect • LPARs with low zIIP usage sharing a zIIP • Especially with a low weight • Potential high latency in logical zIIP being dispatched • If other LPARs have the zIIP • In multiple zIIP case Hiperdispatch can help • “Corrals” work into fewer logical ( & physical) zIIPs • But e.g. 1-Way Queuing regime has unhelpful characteristics • zIIP Parking rarely seen • Of especial concern: • Single zIIP LPAR with low weight and only “DBM1 Engines” exploiter • Consider not configuring the zIIP to the LPAR 29
- 32. zIIP To GCP Ratios • What's most important is how the zIIP performs • Especially how CPU-stringent workloads perform • Extreme case 12 : 1 GCP : zIIP ratio especially unhelpful because of the “1” • An unscientific view is that somewhere in the region of 2 : 1 to 4 : 1 is rarely harmful • Consider both “in LPAR” and “across the machine” effects • Sometimes the answer will be “no zIIPs for this LPAR” 30
- 33. Subcapacity General Purpose Processors • zIIP runs at full speed • e.g. about twice as fast as a 6xx General Purpose Processor (GCP) • Good news: • zIIP higher capacity and faster than GCP • Not so good news: • zIIP-eligible work running on a GCP is worse • Variability in speed if some runs on zIIP and some not • Not terribly different to DDF situation since PM12256 • How this plays depends on numbers of threads and CPU-intensiveness • CPU Conversion Factor: • Use R723NFFS to convert zIIP CPU to GCP equivalent (and vice versa) • Consider configuring more zIIPs than raw capacity requirement suggests • SMT for zIIPs might counteract slower GCPs to some extent 31
- 34. Service-Class Level HonorPriority • Introduced with OA50845 / OA50953 • Prevents “needs help” processing by GCPs • Meaning: Prevents ”cross over” • Ostensibly for Spark • Spark highly zIIP-eligible • Can use a lot of CPU • Also has a Memory Capping function • SMF 30 has a flag for this • At the address space level • Could, in principle, be applied to non-Spark work • Example: Protect DBM1 from “Rogue DDF” work • Note: As zIIP eligibility is “all or nothing” for a DDF thread will only be partial answer • See “(Even) More Fun With DDF” presentation 32
- 35. zIIP And DB2 Accounting Trace • zIIP Eligibility complex question for DB2 work • DB2 Accounting Trace useful here • With Trace Classes 1,2,3: • QWACCLS1_zIIP - Class 1 zIIP Time • QWACCLS2_zIIP - Class 2 zIIP Time • QWACTRTT_zIIP - Trigger zIIP Time • QWACSPNF_zIIP - Stored Procedure zIIP Time • QWACUDFNF_zIIP DS CL8 - User Defined Function (UDF) zIIP Time • QWACZIIP_ELIGIBLE DS - zIIP-on-GCP Time • With Trace Classes 7,8: • QPACCLS7_zIIP - Package-level zIIP Time 33
- 36. If You Only Remember 4 Things The Importance Of zIIP Capacity Planning Recentish News DB2 Criticality So Let's Take This Seriously... Miscellaneous Topics Conclusion Appendix - DB2 Address Spaces (Thanks To John Campbell) 34
- 37. If You Only Remembered 4 Things I Hope They Were • Capacity Planning for zIIPs has become much more important • Pay especial attention to what % Busy represents “full” • Measure zIIP potential and usage down to the address space level • Consider LPAR configuration carefully for zIIPs 35
- 38. If You Only Remember 4 Things The Importance Of zIIP Capacity Planning Recentish News DB2 Criticality So Let's Take This Seriously... Miscellaneous Topics Conclusion Appendix - DB2 Address Spaces (Thanks To John Campbell) 36
- 39. Why Protect DB2 System Address Spaces From Being Pre-empted? 1 / 2 • MSTR contains the DB2 system monitor task • Monitors CPU stalls & virtual storage constraints • DBM1 manages DB2 threads & critical for local DB2 latch & cross-system locking negotiation • Delays in negotiating a critical system or application resource can lead to a slowdown of the whole DB2 data sharing group • Example: P-lock on a space map page 37
- 40. Why Protect DB2 System Address Spaces From Being Pre-empted? 2 / 2 • DIST & WLM-Managed Stored Procedure Server AS only run the DB2 service tasks • i.e. work performed for DB2 not attributable to a single user • Classification of incoming workload, scheduling of external stored procedures, etc. • Typically means these address spaces place a minimal CPU load on the system • But they do require minimal CPU delay to ensure good system wide performance • The higher CPU demands to run DDF and/or SP workloads are controlled by the WLM service class definitions for the DDF enclave workloads or the other workloads calling the SP • Clear separation between DB2 services which are long-running started tasks used to manage the environment and transaction workloads that run and use DB2 services 38
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