New Optimizer Features in Oracle 12c

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1 SAGE Computing Services Customised Oracle Training Workshops and Consulting New Optimizer Features in Oracle 12c Penny Cookson SAGE Computing Services

2 Penny Cookson SAGE Computing Services Customised Oracle Training Workshops and Consulting Managing Director and Principal Consultant Working with Oracle products since 1987 Oracle Magazine Educator of the Year

3 SAGE Computing Services Customised Oracle Training Workshops and Consulting

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5 Stopping the worst stuff ups (1 st time) Adaptive Optimisation Agenda Optimizer Statistics Adaptive Plans X Dynamic X X X X X Sampling X X X X X Dynamic Statistics Cardinality X X X X X X Feedback X X X X X Statistics Feedback SQL Plan directives Other Stuff VARCHAR2 Better histograms Bulk Loads Automatic creation of column statistics groups Session-private statistics for global temporary tables Reporting Mode Reporting on Past Operations

6 Plan A looking good Plan A looking goodgoing to work

7 Now witness the firepower of this fully ARMED and OPERATIONAL battle station! That s Adaptive Optimisation And you really need to try Plan B You know that moment when you realise that Plan A is not going to work

8 Adaptive Optimization Adaptive Plans During optimization not re-optimization Join methods (Hash and NL) and Parallel distribution methods Sub Plan (A) Nested Loop Sub Plan (B) Hash You will find that it is you who are mistaken, about a great many things

9 Adaptive Optimization Adaptive Plans Collector gathers statistics during execution Start reading rows <threshold >=threshold Sub Plan (A) Nested Loop Sub Plan (B) Hash During execution you realise you have underestimated the power of the Hash Side

10 Adaptive Optimization Adaptive Plans Read rows Next time it just chooses the same plan Everything is <threshold >=threshold Sub Plan (A) Nested Loop Sub Plan (B) Hash proceeding as I have foreseen

11 Adaptive Plans - Example name = 'Australian Medical Systems' Organisations Resources This IS the join we are looking for Events Bookings _Large comments = 'TEST' description = 'Buffet Lunch'

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16 This is the default plan for the join to BOOKINGS_LARGE

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18 You have learned much young optimizer

19 What is the Threshold trace Join order[4]: ORGANISATIONS[O]#0 EVENTS_LARGE[E]#2 BOOKINGS_LARGE[B]#3 RESOURCES[R]#1. Outer table: ORGANISATIONS Alias: O resc: 3.00 card 1.00 bytes: 26 deg: 1 resp: 3.00 Inner table: EVENTS_LARGE Alias: E resc: card: bytes: 17 deg: 1 resp: How many Events are we expecting using dmeth: 2 #groups: 1 Cost per ptn: 0.21 #ptns: 1 hash_area: 203 (max=25600) buildfrag: 1 probefrag: 267 ppasses: 1 Hash join: Resc: Resp: [multimatchcost=0.00] HA Join HA cost: resc: resc_io: resc_cpu: resp: resp_io: resp_cpu: Best:: JoinMethod: Hash Cost: Degree: 1 Resp: Card: Bytes: 43

20 What is the Threshold trace *************** Now joining: BOOKINGS_LARGE[B]#3 *************** Outer table: EVENTS_LARGE Alias: E resc: card bytes: 43 deg: 1 resp: Inner table: BOOKINGS_LARGE Alias: B resc: card: bytes: 19 deg: 1 resp: works out the best join order.. ********************************* Number of join permutations tried: 20 *********************************. Searching for inflection point (join #1)

21 expect? What if there are less Events than we expect? Searching for inflection point (join #2) between 0.00 and AP: Computing costs for inflection point at min value 0.00 DP: Using binary search for inflection point search DP: Costing Nested Loops Join for inflection point at card DP: Costing Hash Join for inflection point at card DP: Costing Nested Loops Join for inflection point at card DP: Costing Hash Join for inflection point at card DP: Costing Nested Loops Join for inflection point at card DP: Costing Hash Join for inflection point at card DP: Found point of inflection for NLJ vs. HJ: card =

22 If more than 164 rows you have a hash join you will do

23 BEGIN dbms_spd.flush_sql_plan_directive; END; / Is the information saved? SELECT d.directive_id, d.type, d.state, d.reason, d.created, o.object_name, o.subobject_name, o.notes, o.owner FROM dba_sql_plan_directives d, dba_sql_plan_dir_objects o WHERE o.directive_id = d.directive_id AND o.owner NOT IN ('XDB','SYS','SYSTEM') ORDER BY directive_id desc;

24 Adaptive Optimisation OPTIMIZER_FEATURES_ENABLE >= OPTIMIZER_ADAPTIVE_FEATURES = true OPTIMIZER_ADAPTIVE_REPORTING_ONLY = false Always in motion is the Oracle version

25 Adaptive Optimisation SELECT DBMS_XPLAN.DISPLAY_CURSOR ('89xrxq7gghfdm',0, FORMAT=>'+REPORT') FROM dual;

26 Statistics Feedback

27 Storm Trooper Conference How many chairs do we need in the main room? Base it on our existing statistics

28 Storm Trooper Conference This should be enough

29 Oh dear who knew Connor McVader was presenting

30 Storm Trooper Conference How many chairs do we need in the main room? Base it on our existing statistics and the feedback from this morning

31 That s better, but what happens when they shut the place down and we start again tomorrow?

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33 plan o problem we have obeyed the xxxxxxxx prime directive

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36 1010 is a minority value Statistics are not up to date When will statistics feedback be used?

37 Find the SQL_ID

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40 Execute again but it uses the same plan Cardinality feedback not used

41 With a complex condition

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44 Execute again

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47 After executing the same statement again

48 Statistics Feedback works with Joins too now it does And persistent it is

49 Dynamic Statistics Dynamic stats considered when: OPTIMIZER_DYNAMIC_SAMPLING = default (2) DYNAMIC_SAMPLING hint Parallel No/old statistics Expressions Complex predicates (OR or AND on 1 table) Joins/Group By (12) Automatic dynamic sampling for level 11 (12) Shareable

50 Table has no statistics Default value (2) for OPTIMIZER_DYNAMIC_SAMPLING

51 Access the table that has no statistics

52 Table that has really bad statistics

53 Access the table that has bad statistics

54 Statistics are up to date, but we have a complex condition

55 Statistics are up to date, but we have a complex condition But no dynamic sampling

56 Dynamic Statistics When should we use them? Stats not right Unknown conditions Stable table Get a new DBA Volatile table TP Dynamic stats at session/task level TP or DWH database? DWH Dynamic stats at DB level TP or DWH database? DWH TP Get a new DBA

57 Shareable Dynamic Statistics

58 SQL Plan directives Adaptive Optimisation Summary During Execution NL or Hash Adaptive Plans Adaptive Statistics Parallel distribution Dynamic statistics Cardinality

59 Adaptive Optimisation Summary Re-optimisation Next hard parse SQL Plan directives Statistics feedback Only SQL Plan Management deals in absolutes Dynamic Statistics

60 Adaptive Optimisation Summary Feature Bind Vars /Literals Conditions When Adaptive Plan Literals and bind variables Join method, Parallelisation During Statistics Feedback Literals but works with Adaptive cursors for bind variables Complex conditions joins Re-Opt but stores as SPD Adaptive cursor Bind variables Skewed data and histogram During - /*+BIND_AWARE */ Or Re-opt Dynamic Statistics Literals and Bind Variables Dependent on level no stats, old stats, complex conditions During

61 Optimisation Enhancements Adaptive optimisation is good for the multi table dependencies that statistics cannot help with Need for some statistics feedback can be removed by correct statistics watch the plan directives Dynamic stats can help with weird query combinations and volatile tables

62 Monitor SQL Plan Directives you must Help you improve your statistics they will

63 Improved Statistics Male Jedis always say that. It matters to the optimizer Size matters not. Look at me. Judge me by my size, do you?

64 11g -Histograms 11g -Histograms 7 distinct values 7 buckets Frequency Histogram

65 11g -Histograms 11g -Histograms Height Balanced Histogram 7 distinct values 6 buckets

66 2g -Histograms 7 distinct values 5 buckets Top 5 values occurs >= (1 1/5)*100 pct = 80% estimate_percent = AUTO_SAMPLE_SIZE Top Frequency Histogram

67 12g -Histograms Hybrid Histogram Repeat Count distinct values 5 buckets Top 5 values occurs < (1 1/5)*100 pct = 80%

68 12g -Histograms Height balanced histograms stop using you should Estimate_percent = integer do not use

69 Extended Statistics Introduced in 11g for multi column data dependencies

70 Data Dependency SELECT count(*) FROM org WHERE state = WA and postcode = 6000

71 11g Create Statistics on a Column Group dbms_stats.create_extended_stats ('TRAIN', ORG','(STATE, POSTCODE)');

72 12c Create Statistics on a Column Group

73 12c Create Statistics on a Column Group

74 12c Create Statistics on a Column Group

75 12c Use Statistics on a Column Group

76 Running Statistics in Reporting Mode SET LINES 100 PAGES 0 SET LONG COLUMN REPORT FORMAT A200 VARIABLE stats_report CLOB; BEGIN :stats_report := dbms_stats.report_gather_schema_stats (ownname=>'train', detail_level=>'all', format=>'html'); END;

77 Running Statistics in Reporting Mode

78 Reporting on Past Statistics SET LINES 100 PAGES 0 SET LONG COLUMN REPORT FORMAT A200 VARIABLE stats_report CLOB; BEGIN :stats_report := dbms_stats.report_stats_operations (since=>sysdate-2, until=>sysdate, detail_level=>'all', format=>'html'); END;

79 Global Temporary Tables - Oracle 11.2

80 Oracle 11.2 New Session

81 Oracle 11.2 Original Session ( rows) Those were not the statistics we were looking for

82 Global Temporary Tables - Oracle 11.2 R2-D2, you know better than to trust a strange computer

83 Session specific statistics for global temporary tables Session specific statistics on global temporary tables

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85 Consider gathering statistics you should when Global Temporary Tables you are working with

86 Online Statistics Gathering for Direct Load Oracle 11g Load and then gather stats Extra full scan

87 Oracle 12c Statistics automatically gathered

88 But no histogram

89 Create a table and index, then populate it

90 Table/column statistics are created

91 Index stats not created

92 Create a table and insert one row

93 We have the statistics from the CREATE

94 Deceive you your eyes can; do not trust them Now append a whole load of rows

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96 It still thinks the table is empty

97 Increase in Limit for VARCHAR2 ID COMMENTS ID COMMENTS 13 XXXX XXXX 14 XXXX XXXX 15 XXXX XXXX 13 XXXX XXXX XXXXXXX XXXXXXX XX 14 XXXX XXXX XXXXXXX XXXXXXX XX 15 XXXX XXXX XXXXXXX XXXXXXX XX VARCHAR2(4000) VARCHAR2(32767)

98 You can't stop change any more than you can stop the suns from setting DBA Morning Tea Master Yoda says I should be mindful of the future The optimizer is much smarter But what about stability? Questions? But not at the expense of the moment