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DB2 Through My Eyes

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My "DB2 Through My Eyes" presentation as given in Dublin, May 2015

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DB2 Through My Eyes

  1. 1. Session zPE2235 : DB2 Through My Eyes Martin Packer martin_packer@uk.ibm.com
  2. 2. Abstract Bridging the gap in perspectives between DB2 and System Performance specialists is a perennial concern of mine: As a specialist in one you're much more valuable if you can bridge that gap. This presentation shows some techniques I use to understand a customer's DB2 environment before I talk to a customer's DB2 specialists (or indeed my own). All these techniques are available to you, the data being readily available. I hope you find them useful.
  3. 3. What Is DB2? (for the purposes of this discussion)
  4. 4. Subsystems
  5. 5. CPU
  6. 6. CPU ... ● Track CPU by e.g. Time Of Day – Regular variations – Spikes ● Detect split between e.g. zIIP-eligible and non- – For example, Prefetch and Deferred Write might fall away at certain times – What is a reasonable expectation? ● Notice when zIIP-eligible work ends up on GCPs ● For DIST detect when non-Enclave work is large – Might suggest issues with e.g. Authentication
  7. 7. © 2014 IBM Corporation8 A DB2 Version DBM1 Address Space's zIIP and CPU Usage Over 24 Hours
  8. 8. Real Memory ● SMF 30 data useless for real memory – Memory service declines if CPU queuing experienced ● Use SMF 72 Subtype 3 – Reporting Class for individual or groups of DB2 subsystems – Vast majority will be DBM1 ● Use DB2 IFCID 225 data – Accurate real memory statistics
  9. 9. Virtual Memory ● SMF 30 shows allocated – Above and below the line ● High and Low – 64-Bit – Accurate - so far as it goes - for all address spaces ● Use DB2 IFCID 225 data – Accurate virtual memory statistics for DBM1 – IRLM, MSTR, DIST much smaller ● Use DB2 Statistics Trace for area usage / value
  10. 10. I/O ● Both “system” and “database” I/O best represented by SMF 42-6 ● Database and Table Space / Index Space encoded in data set qualifiers – Relatable to buffer pool by the DB2 Catalog ● Looking for: – I/O rate – cacheability* – Read / Write ratio – Components of response time * Caution over Sync Remote Copy Disconnect Time
  11. 11. Coupling Facility
  12. 12. Parallel Sysplex – Coupling Facility ● 3 types of Coupling Facility structure: – GBPs, LOCK1, SCA – Often duplexed – Configurations vary considerably ● Lots of useful information – e.g. LOCK1 False Contention – e.g. Group Buffer Pool sizing & Data / Directory split ● Augment with DB2 Statistics Trace perspective
  13. 13. XCF
  14. 14. Parallel Sysplex - XCF ● Most traffic in support of LOCK1 – IXCLOmmm – Telling XES Contention from False ● Latter usually caused by Lock structure being too small – DXRnnnnn – Telling IRLM Contention from XES ● Understand how traffic varies with time of day ● Note: XCF member job name in R742MJOB
  15. 15. Stored Procedures ● Native run in DBM1 address space ● Others run in Server Address Spaces – Stored procedure defined with Application Environment – Caller runs in a Service Class – Queue serves combination of SC and AE – WLM starts and stops address spaces ● PGM=DSN9XWLM ● Can see e.g. CPU, virtual storage, EXCPs, Unix statistics in SMF 30 – Data set in SMF 42-6 ● Normally I roll up all address spaces with same name – Probably not a good idea for server address spaces – Not rolling up yields start / stop timestamps, balance – Population might be important and roll up is fine for this
  16. 16. Applications
  17. 17. Application – SMF 30 Usage Data Section
  18. 18. Application Performance - Using SMF 101 ● CPU usage and lots of elapsed time buckets – With Trace Classes 1,2,3 – Down to program (Package) with 7,8 ● SQL counts at program level with 10 ● For Interactive – Granularity down to eg CICS Transaction and Program ● For DDF – The SMF way to detect DDF access to a DB2 – Lots of identifiers ● Suitable for encoding in WLM Policy
  19. 19. Accounting Trace (SMF 101) - Batch
  20. 20. Specialist Subjects
  21. 21. Workload Manager ● SMF 30 identifies Workload, Service Class, Report Class – I use this to establish if eg DBM1 well classified ● DDF requires Accounting Trace – QWACWLME field – Allows analysis of what DDF work comes in and how it's classified ● WLM ISPF TLIB tells me the rules
  22. 22. Rules Goal
  23. 23. DDF Rules
  24. 24. Restarts ● SMF 30 has Reader Start Time – Can compare to IPL – No customer (yet) restarts Production DB2 daily ● Some restart weekly or fortnightly ● Some have been up for months – My parallel sysplex customers roll round the sysplex Gap because I have data from Weds onwards
  25. 25. Conclusion ● “A bridge, not a bypass” ● In a “cloudier” world detecting e.g. DB2 subsystems without specialist instrumention is valuable. ● Understanding what's normal is valuable – Especially if you can do it with little effort

My "DB2 Through My Eyes" presentation as given in Dublin, May 2015

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