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Using SQL Plan Management (SPM) to Balance Plan Flexibility and Plan Stability
- 1. Using SQL Plan Management (SPM) to balance Plan Flexibility and Plan Stability Carlos Sierra
- 2. Carlos Sierra • SQLTXPLAIN + SQL Health-‐Check SQLHC + • Consultant/Developer/DBA/Design/+ • Oracle Performance + SQL Tuning • Oracle Database Health-‐Check • Tools + Scripts • Speaker Enkitec (c) 2014 2
- 3. Topics • MoPvaPon • SQL Plan Management (SPM) – Mechanics – Demos Enkitec (c) 2014 3
- 4. Plan Flexibility • Cost-‐based OpPmizer (CBO) – Introduced in Oracle 7 – Computes an OpPmal Plan based on • HeurisPcs • Query Predicates • Schema Object StaPsPcs • Several Others Enkitec (c) 2014 4
- 5. Flexibility: Good or Evil? • CBO Mission – Compute an OpPmal Plan for a given SQL and its Data • Plans have many and complex Dependencies • CBO Performance – Successful most of the Pmes • Produces a sub-‐opPmal Plan some,mes Enkitec (c) 2014 5
- 6. DBA Recurrent Nightmare • A business criPcal process experiences an occasional slow down – Same SQL usually runs quickly – Developers claim they haven’t changed anything – Users claim they do the same every Pme – Business keeps reporPng this: to YOU! Enkitec (c) 2014 6
- 7. Why Plans Perform Inconsistently? (1) • Concurrency with some other Process • State of Buffer Cache • RAC Node Affinity • CPU StarvaPon • Sudden Changes on Data Volume • Inconsistent Performance through Database Link Enkitec (c) 2014 7
- 8. Why Plans Perform Inconsistently? (2) • Downgraded Parallel ExecuPon • Crossing Small-‐Table Threshold • Resource Manager DirecPve • Plan Flips • Many Others… Enkitec (c) 2014 8
- 9. Why a Plan Flips? (1) • Bind Variable Peeking with Histograms • Outdated Schema Object (SO) StaPsPcs • Missing SO StaPsPcs • Fresh SO StaPsPcs • New Empty ParPPons Enkitec (c) 2014 9
- 10. Why a Plan Flips? (2) • Incomplete set of CBO Hints – Either on SQL Text or SQL Profile • Dropped, Invalid, Invisible or new Indexes • Index or Table rebuild • Two or more Plans with similar Cost Enkitec (c) 2014 10
- 11. Why a Plan Flips? (3) • Database Parameters Changes • CBO System StaPsPcs Changes • Asynchronous SO StaPsPcs Gathering • Many Others… Enkitec (c) 2014 11
- 12. How to MiPgate Plan Flipping? • Solid CBO StaPsPcs • Default CBO Parameters • Avoid Global Changes Enkitec (c) 2014 12
- 13. Plan Flexibility Allies • CBO Parameters • CBO StaPsPcs • Dynamic Sampling • Cardinality Feedback • Cursor Sharing • Adap0ve Cursor Sharing (ACS) Enkitec (c) 2014 13
- 14. Plan Stability Tools • CBO Hints • Stored Outlines • SQL Profiles • SQL Plan Management (SPM) Enkitec (c) 2014 14
- 15. SQL Plan Management • 11g+ • MulPple Persistent OpPmal ExecuPon Plans per SQL • Only “accepted” and “enabled” Plans are Executed • New Plans are acknowledged but not Executed • Goal: Plan Stability with controlled Flexibility Enkitec (c) 2014 15
- 16. SQL Plan Baseline • A set of Plans available to the CBO for a given SQL – IdenPfied by SQL Handle and Signature • Hash funcPon on SQL Text • dbms_sqltune.sqltext_to_signature – View dba_sql_plan_baselines • enabled = YES • accepted = YES • reproduced = YES Enkitec (c) 2014 16
- 17. Plan History • Content of dba_sql_plan_baselines • Includes SQL Plan Baseline • Includes Pending Plans – accepted = NO and last_verified is NULL • Includes Rejected Plans – accepted = NO and last_verified is not NULL • Includes Disabled Plans Enkitec (c) 2014 17
- 18. Methods to Create a Plan Baseline 1. Capture 2. Load a. Cursor Cache (CUR) b. SQL Tuning Set (STS) c. Stored Outline 3. MigraPon Enkitec (c) 2014 18 1. Capture 2. Load a. CUR b. STS c. AWR d. SPA e. TRC 3. MigraPon
- 19. Capturing a SQL Plan Baseline (1) • Set opPmizer_use_sql_plan_baselines to TRUE (default) • Set opPmizer_capture_sql_plan_baselines to TRUE (default is FALSE) – Set this parameter at SESSION level • Execute SQL 2 Pmes • Set opPmizer_capture_sql_plan_baselines to FALSE Enkitec (c) 2014 19
- 20. Capturing a SQL Plan Baseline (2) Enkitec (c) 2014 20
- 21. Loading SQL Plan Baseline from Cache • dbms_spm.load_plans_from_cursor_cache – Inputs • sql_id • plan_hash_value (opt) – Outputs • Number of Plans loaded Enkitec (c) 2014 21
- 22. 22 DBMS_SPM.LOAD_PLANS_FROM_CURSOR_CACHE ( sql_id IN VARCHAR2, plan_hash_value IN NUMBER := NULL, sql_text IN CLOB, fixed IN VARCHAR2 := 'NO', enabled IN VARCHAR2 := 'YES') RETURN PLS_INTEGER; DBMS_SPM.LOAD_PLANS_FROM_CURSOR_CACHE ( sql_id IN VARCHAR2, plan_hash_value IN NUMBER := NULL, sql_handle IN VARCHAR2, fixed IN VARCHAR2 := 'NO', enabled IN VARCHAR2 := 'YES') RETURN PLS_INTEGER; DBMS_SPM.LOAD_PLANS_FROM_CURSOR_CACHE ( sql_id IN VARCHAR2, plan_hash_value IN NUMBER := NULL, fixed IN VARCHAR2 := 'NO', enabled IN VARCHAR2 := 'YES') RETURN PLS_INTEGER; DBMS_SPM.LOAD_PLANS_FROM_CURSOR_CACHE ( attribute_name IN VARCHAR2, attribute_value IN VARCHAR2, fixed IN VARCHAR2 := 'NO', enabled IN VARCHAR2 := 'YES') RETURN PLS_INTEGER; Enkitec (c) 2014 One of possible attribute names: • 'SQL_TEXT' (like) • 'PARSING_SCHEMA_NAME' (equality) • 'MODULE' (equality) • 'ACTION' (equality) SQL text to use in identifying the SQL plan baseline into which the plans are loaded. If the SQL plan baseline does not exist, it is created. The use of text is crucial when the user tunes a SQL statement by adding hints to its text and then wants to load the resulting plan(s) into the SQL plan baseline of the original SQL statement. SQL handle to use in identifying the SQL plan baseline into which the plans are loaded. The sql_handle must denote an existing SQL plan baseline. The use of handle is crucial when the user tunes a SQL statement by adding hints to its text and then wants to load the resulting plan(s) into the SQL plan baseline of the original SQL statement. Plan identifier. Default NULL means capture all plans present in the cursor cache for the SQL statement identified by SQL_ID.
- 23. SQL Plan Baseline Loading OpPons • Load a Plan from a Hinted version of a SQL into SQL Baseline of Original SQL – Use SQL Text if there is no pre-‐exisPng SQL Baseline – Use SQL Handle if SQL Baseline already exists • Load one or more Cursor Plans (memory) for a SQL • Load Plans for Subset of Cursors based on Schema, SQL Text “like” or ApplicaPon (Module or AcPon) Enkitec (c) 2014 23
- 24. Demo 6 • Load Plans for Query out of Demo 5 – demo5.sql (1st Pme) – load_plans.sql • Execute Demo 5 again and review Plan History – demo5.sql (2nd Pme) – list_plans.sql • Execute demo5.sql 2x (3rd & 4th) and verify results Enkitec (c) 2014 24
- 25. Demo 6 Results (aqer 3rd demo5.sql) CHILD EXECUTIONS BUFFER_GETS PLAN_HASH_VALUE SHAR SENS AWRE -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐ -‐-‐-‐-‐ -‐-‐-‐-‐ 0 3 9090 3600618656 Y Y N CHILD BUCKET_ID COUNT -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ 0 0 0 0 1 1 0 2 2 Note -‐-‐-‐-‐-‐ -‐ SQL plan baseline SQL_PLAN_652hmt7yxthdwc0e59472 used for this statement CREATED PLAN_NAME ENA ACC REP FIX -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐ -‐-‐-‐ -‐-‐-‐ -‐-‐-‐ 21-‐JUN-‐14 02.00.10.000000 PM SQL_PLAN_652hmt7yxthdw80508062 YES YES YES NO 21-‐JUN-‐14 02.00.10.000000 PM SQL_PLAN_652hmt7yxthdwc0e59472 YES YES YES NO 21-‐JUN-‐14 02.00.10.000000 PM SQL_PLAN_652hmt7yxthdwe00bee24 YES YES YES NO 21-‐JUN-‐14 02.00.19.000000 PM SQL_PLAN_652hmt7yxthdwc82a6b0c YES NO YES NO Enkitec (c) 2014 25
- 26. Demo 6 Results (aqer 4th demo5.sql) CHILD EXECUTIONS BUFFER_GETS PLAN_HASH_VALUE SHAR SENS AWRE -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐ -‐-‐-‐-‐ -‐-‐-‐-‐ 0 2 723482 847574763 N Y N 1 1 2404 3600618656 Y Y Y 2 1 1977 189372815 Y Y Y 3 1 568 847574763 Y Y Y Note -‐-‐-‐-‐-‐ -‐ SQL plan baseline SQL_PLAN_652hmt7yxthdw80508062 used for this statement CREATED PLAN_NAME ENA ACC REP FIX -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐ -‐-‐-‐ -‐-‐-‐ -‐-‐-‐ 28-‐DEC-‐13 02.03.43.000000 PM SQL_PLAN_652hmt7yxthdw501f1424 YES YES YES NO 28-‐DEC-‐13 02.03.43.000000 PM SQL_PLAN_652hmt7yxthdwb6c39290 YES YES YES NO 28-‐DEC-‐13 02.03.43.000000 PM SQL_PLAN_652hmt7yxthdwd624c0cd YES YES YES NO 28-‐DEC-‐13 02.03.50.000000 PM SQL_PLAN_652hmt7yxthdwc82a6b0c YES NO YES NO Enkitec (c) 2014 26
- 27. Demo 7 • Drop SQL Plan Baseline – drop_plans.sql • Create SQL Patch with /*+ BIND_AWARE */ Hint – sqlpch.sql for 8u0n7w1jug5dg connected as SYS • Load Plans for Query out of Demo 5 – demo5.sql – load_plans.sql Enkitec (c) 2014 27
- 28. Demo 7 Results CHILD EXECUTIONS BUFFER_GETS PLAN_HASH_VALUE SHAR SENS AWRE -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐ -‐-‐-‐-‐ -‐-‐-‐-‐ 0 1 2191 847574763 N Y Y 1 1 3030 2048551027 Y Y Y 2 1 2404 3600618656 Y Y Y 3 1 1977 189372815 Y Y Y 4 1 568 847574763 Y Y Y CREATED PLAN_NAME ENA ACC REP FIX -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐ -‐-‐-‐ -‐-‐-‐ -‐-‐-‐ 21-‐JUN-‐14 02.09.14.000000 PM SQL_PLAN_652hmt7yxthdw80508062 YES YES YES NO 21-‐JUN-‐14 02.09.14.000000 PM SQL_PLAN_652hmt7yxthdwc0e59472 YES YES YES NO 21-‐JUN-‐14 02.09.14.000000 PM SQL_PLAN_652hmt7yxthdwc82a6b0c YES YES YES NO 21-‐JUN-‐14 02.09.14.000000 PM SQL_PLAN_652hmt7yxthdwe00bee24 YES YES YES NO Enkitec (c) 2014 28
- 29. Demo 8 • Execute queries 1-‐5 and observe how number of ExecuPons increases per Child Cursor – flush.sql – demo8.sql – demo8.sql – demo8.sql Enkitec (c) 2014 29
- 30. Demo 8 Results CHILD EXECUTIONS BUFFER_GETS PLAN_HASH_VALUE SHAR SENS AWRE -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐ -‐-‐-‐-‐ -‐-‐-‐-‐ 0 1 3030 2048551027 Y Y Y 1 1 2404 3600618656 Y Y Y 2 1 1977 189372815 Y Y Y 3 1 568 847574763 N Y Y 4 1 724 847574763 Y Y Y Note -‐-‐-‐-‐-‐ -‐ SQL patch "sqlpch_8u0n7w1jug5dg" used for this statement -‐ SQL plan baseline SQL_PLAN_652hmt7yxthdwb6c39290 used for this statement CHILD EXECUTIONS BUFFER_GETS PLAN_HASH_VALUE SHAR SENS AWRE -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐ -‐-‐-‐-‐ -‐-‐-‐-‐ 0 2 6060 2048551027 Y Y Y 1 2 4808 3600618656 Y Y Y 2 2 3954 189372815 Y Y Y 3 1 568 847574763 N Y Y 4 3 2016 847574763 Y Y Y Enkitec (c) 2014 30
- 31. Evolving a Plan (1) • Evolving a Plan means “accepPng” it – PromoPng it from Plan History into SQL Plan Baseline • dbms_spm.evolve_sql_plan_baseline – sql_handle (opt) – plan_name (opt) – verify (default YES) – commit (default YES) Enkitec (c) 2014 31
- 32. Enkitec (c) 2014 32 DBMS_SPM.EVOLVE_SQL_PLAN_BASELINE ( sql_handle IN VARCHAR2 := NULL, plan_name IN VARCHAR2 := NULL, time_limit IN INTEGER := DBMS_SPM.AUTO_LIMIT, verify IN VARCHAR2 := 'YES', commit IN VARCHAR2 := 'YES') RETURN CLOB; DBMS_SPM.EVOLVE_SQL_PLAN_BASELINE ( plan_list IN DBMS_SPM.NAME_LIST, time_limit IN INTEGER := DBMS_SPM.AUTO_LIMIT, verify IN VARCHAR2 := 'YES', commit IN VARCHAR2 := 'YES') RETURN CLOB; Evolving a Plan (2)
- 33. Demo 9 • Drop SQL Plan Baseline – drop_plans.sql • Capture SQL Plan Baseline with 1 accepted Plan – demo9.sql – list_plans.sql • Evolve all Plans on Plan History – evolve.sql Enkitec (c) 2014 33
- 34. FIXED Flag • When set to YES – Only FIXED Plans are considered for Plan SelecPon – No more Plans are Captured into Plan History Enkitec (c) 2014 34
- 35. Alter SQL Plan Baselines Enkitec (c) 2014 35 DBMS_SPM.ALTER_SQL_PLAN_BASELINE ( sql_handle IN VARCHAR2 := NULL, plan_name IN VARCHAR2 := NULL, attribute_name IN VARCHAR2, attribute_value IN VARCHAR2) RETURN PLS_INTEGER; Attribute Names & Values: enabled 'YES' or 'NO' fixed 'YES' or 'NO' autopurge 'YES' or 'NO' plan_name String of up to 30-‐characters description String of up to 500-‐characters
- 36. Plan SelecPon (1) • At hard parse when SQL Plan Baseline (SPB) exists 1. CBO computes an “OpPmal” Plan (OP) • AdapPve Cursor Sharing is used if applicable 2. If OP exists in SPB then execute this OP 3. If OP does not exist in SPB then store it in Plan History a. If there are FIXED Plans in SPB i. Re-‐cost all FIXED Plans using Binds and execute cheapest b. If there are no FIXED Plans in SPM i. Re-‐cost all Plans using Binds and execute cheapest Enkitec (c) 2014 36
- 37. Plan SelecPon (2) Enkitec (c) 2014 37
- 38. Demo 10 • FIX one Plan from SQL Plan Baseline – alter_plans.sql • Verify only one Plan was Executed – flush.sql – demo8.sql – demo8.sql Enkitec (c) 2014 38
- 39. SPM Summary Enkitec (c) 2014 39 • SPM provides much desired Plan Stability – Only “approved” Plans are allowed to Execute • ACS can generate a healthy stock of OpPmal Plans – You can restrict them to work under SPM • Combining ACS and SPM you can obtain – Plan Flexibility and Plan Stability
- 40. ACS Suggested Strategy • Use sys.dbms_sqldiag_internal.i_create_patch to SQL Patch with BIND_AWARE the SQL on Baselines • Use free script sqlpch.sql Enkitec (c) 2014 40
- 41. SPM Suggested Strategies 1. ConservaPve – One SQL at a Pme 2. Moderate – One ApplicaPon at a Pme (Module or AcPon) – One Schema at a Pme 3. Aggressive (a.k.a. Cowboy method) – All ApplicaPon Schemas at once Enkitec (c) 2014 41
- 42. Oracle Pack Licenses • DBMS_SPM – No Oracle Pack License • DBMS_SQLTUNE – Oracle Tuning Pack • AWR – Oracle DiagnosPcs Pack Enkitec (c) 2014 42
- 43. References (1) • Random Slowdown by Jonathan Lewis – hvp://jonathanlewis.wordpress.com/2013/12/23/ plan-‐changes/ • SQL Plan Management SPM Aware OpPmizer – hvps://blogs.oracle.com/opPmizer/entry/ sql_plan_management_part_2_of_4_spm_aware_opP mizer Enkitec (c) 2014 43
- 44. References (2) • Oracle® Database PL/SQL Packages and Types Reference – 11g Release 2 (11.2) – Part Number E25788-‐04 Enkitec (c) 2014 44
- 45. Contact InformaPon • carlos.sierra@enkitec.com • carlos-‐sierra.net • @csierra_usa Enkitec (c) 2014 45