Presentation on Oracle memory optimization. Presented at Perth AUSOUG 20/20 Conference November 2009.

1. Thanks for the Memory Guy Harrison Director, Melbourne R&D guy.harrison@quest.com www.guyharrison.net

2. Introductions Buy Quest Products

3. Human memory is complex Short Term Sensory Store: ~ 1 second uncompressed raw memory Working memory: Limited capacity, requires attention Long term memory: physically stored in brain structure; large capacity; indexed strangely Beyond Bullets Points: By: Cliff Atkinson

5. PGA is used for program working memory such as sorting and hashing

7. What consumes PGA memory Sorts: ORDER BY SORT-MERGE JOIN UNION, INTERSECT, MINUS Pre-10GR2 GROUP BY , DISTINCT Analytic functions: OVER(), LEAD(), LAG(), etc Hash Operations: Hash join Hash GROUP BY, DISTINCT PL/SQL variables Collections BULK COLLECT Parameter passing without NOCOPY

8. PGA Aggregate Target and session memory

9. Optimal, one-pass, multi-pass Multi-pass Single Pass Optimal

10. Sort merge and hash joins

11. Estimated SQL memory

12. Actual SQL Memory

13. PGA advice - manual

14. PGA advice - OEM

15. PGA and Sorts – Spotlight on Oracle

16. Opting out of PGA Aggregate Target Default workarea sizing policies only allow for a session to get 10-20% of the PGA If a single large sort is in progress, it makes sense to “opt out” of automatic workarea sizing

17. Shared Memory

18. Modified LRU mechanism Oracle Session Buffer Cake Buffer Cache

19. Modified LRU mechanism: Table Scans Oracle Session Buffer Cake Buffer Cache

20. Impact of direct path IO http://guyh.textdriven.com/OPSGSamples/Ch18/temporary_direct.sql

21. The buffer cache “hit rate” http://guyh.textdriven.com/OPSGSamples/Ch18/hit_rate.sql

22. Multiple buffer pools

23. Buffer Cache advisory: manual

24. Buffer cache advisory: OEM

25. Automatic Shared Memory management (ASMM) Default in 10g and recommended (with caveats): Set Minimum values for key pools (buffer pools, shared pool) Manually size non-default pools using V$DB_CACHE_ADVICE Monitor for memory starvation Monitor for memory thrashing Waits on “SGA: allocation forcing component growth”

26. Memory starvation and thrashing

27. Optimizing overall memory Optimizing between PGA and SGA are often more significant than allocating within each area In 10g optimization is difficult: Compare PGA and Buffer Cache advisories Adjust based on IO types (direct read temp vs. physical reads) In 11g can use Automatic Memory Management Risk of thrashing and starvation is greater than with ASMM Set minimum values for all pools Manually configure non-default buffer pools

28. Worst case scenario Trivial memory allocations from PL/SQL programs can steal vital memory from buffer cache Situation can become worse if MTS is enabled Setting minimum values is virtually mandatory

29. Spotlight on Oracle memory management

30. Spotlight on Oracle memory management

31. 11g Result Set Cache Can provide massive improvements for expensive queries on static tables In memory dynamic materialized view?

32. Result set cache Caveats: Single latch on modifications Any modification to a dependent table flushes the result sets Can select statements only at the table level or by inserting a hint Bottom line: Limited effectiveness Unique candidate SQLs must be low frequency Tables must be static

33. Things we didn’t talk about Shared pool Redo buffer Large Pool Flashback buffer

34. Key take aways Don’t emphasize buffer cache tuning at the expense of PGA Consider opting out of PGA Aggregate Target for large sorts ASMM and ASM are fine, but set minimums for important memory pools Result set cache is promising, but right now is of limited applicability

35. End of Presentation