104/22/23

HintsOutlines/Profiles/Baselines

Kyle Haileyhttp://oraclemonitor.com

SQL Plan Stability

When to tune?

• Users complain

• Response times slow

• Resource usage high

• AAS of system is high

• Check OEM

• LIOs high per row, TCF discrepancies high

• script

204/22/23

TCF , LIO and Elapsed

ELAPSED LIO_RW RATIO1 E_ROWS A_ROWS operation---------- ------ ------ ------- ------ --------------------------------- 0 0 1 SELECT STATEMENT 5,720,456 0 1 1 HASH GROUP BY 29,711 0 1,909 NESTED LOOPS 0 0 +++ 1 1,909 NESTED LOOPS 1,969,304 0 +++ 1 1,909 NESTED LOOPS 0 0 +++ 1 2,027 NESTED LOOPS 7,939,649 0 +++ 1 1,656 NESTED LOOPS 716,054 0 +++ 1 1,657 NESTED LOOPS 270,201 0 ++ 39 23,171 HASH JOIN 23 0 5 1 JOIN FILTER CREATE :BF00 31 1 5 1 TABLE ACCESS BY INDEX R 14 2 5 1 INDEX RANGE SCAN PS0PA 141,467 0 18,503 23,171 VIEW VW_SQ_1 3,032,120 0 18,503 23,171 HASH GROUP BY 152,564 0 163,420 33,020 JOIN FILTER USE :BF000 407,746 0 163,420 33,020 MERGE JOIN 55 0 5 1 SORT JOIN 12 2 5 1 INDEX RANGE SCAN PS 79,435 0 40,000 33,020 SORT JOIN 119,852 0 40,000 40,000 INDEX FAST FULL SCA 2,959,031 13 - 23,171 1,657 TABLE ACCESS BY INDEX ROW 944,887 1 23,171 23,174 INDEX RANGE SCAN WB_JOB

304/22/23

How to tune

• Parameters (init.ora, spfile, session level)

• Hacking, global

• Rewrites • Hacking, specific

• Object Stats (Optimizer cardinality and cost calculations)

• Hints (Outlines, Profiles ,Baselines)

• Index (good cluster, bad cluster, index only)

• Partitions, Materialized views, Hash clusters

404/22/23

HINTS

• ORDERED

• Leading(tab_alias, tab_alias, …)

• USE_NL(table_alias) – Inner Table (not driving)

• USE_HASH(table_alias) – 2cd table, probe into

• INDEX(tab_alias index_name)

• NO_MERGE

Oracle first decides join order then join type

(example http://www.adp-gmbh.ch/blog/2008/01/17.php)

504/22/23

Col ACol B

Col C

Join Index

Col D

Table Y

Table X

Filter Index

Col ACol B

Col C

Filter Index

Col D

Table Y

Table X

Filter Index

NL HJDriving Table

Drive from Table Y off of set of rows returned from filter on column CNested loops into Table X on Index on JoinFilter results without Index even though index on filter column

Create hash result set on Table Y from filter on column CProbe hash result set with rows from filter on table X on column A

NL and HJ hints

Nested Loops (start with A probe in B)

/*+ leading(A) use_nl(B) */

/*+ ordered use_nl(B) */

• Hash Join (hash A loop up B in A)

/*+ leading (A) use_hash(B) */

/*+ ordered use_hash (B) */

704/22/23

Select * from A,B where A.f1=B.f1

INDEX HINT

•INDEX(Table_alias INDEX_NAME)

•10g:

• INDEX(table_alias (col1 col2 …)

804/22/23

TCF

• TCF => optimal execution plan path

• How about “Is the access path optimal ?

ie indexes, partitions, constraints

Christian Antognini p341 TOP

• < 5 lio per row

• < 10 lio ok

• > 15 potentially sub-optimal

Outlines, Profiles, Baselines

• Outlines 8i

• Apply a set of hints to query to stabilize plan

• Profiles 10g

• Apply hints to shift statistics to help optimizer

• Use for multiple statements that only differ by literals

• Baselines 11

• Track new plans and “evolve” them if better

1004/22/23

Outline tables

ol$ OL_NAME SQL_TEXT TEXTLEN SIGNATURE HASH_VALUE HASH_VALUE2 CATEGORY VERSION CREATOR TIMESTAMP FLAGS HINTCOUNT SPARE1 SPARE2

1104/22/23

ol$hint OL_NAME HINT# CATEGORY HINT_TYPE HINT_TEXT STAGE# NODE# TABLE_NAME TABLE_TIN TABLE_POS REF_ID USER_TABLE_NAME

COST CARDINALITY BYTES HINT_TEXTOFF HINT_TEXTLEN JOIN_PRED SPARE1 SPARE2 HINT_STRING

ol$nodes OL_NAME

CATEGORY

NODE_ID

PARENT_ID

NODE_TYPE

NODE_TEXTLEN

NODE_TEXTOFF

NODE_NAME

If you drop the hints in ol$hint for a name then rename another set of hints with the old name then the sql text in ol$ will get the new hints

Outline Switching

1204/22/23

Profiles

1304/22/23

Profile Switching

• Get bind variables if necessary

• build_bind_vars.sql 

• Tune query with hints (or any other method)

• Create a profile on the new query

• create_sql_profile.sql  (calls rg_sqlprof1.sql)

• fix the Profile to eliminate any bad index hints -

• fix_sql_profile_hint.sql 

• move the profile over to the original statement

• move_sql_profile.sql

1404/22/23

http://kerryosborne.oracle-guy.com/2009/10/how-to-attach-a-sql-profile-to-a-different-statement-take-2/

SQL Baselines

•Outlines are way outdated in 11g

• they still take precedence over Baselines

•Baselines can be switched between statements even easier than outlines

http://kerryosborne.oracle-guy.com/2009/04/oracle-11g-sql-plan-management-sql-plan-baselines/http://kerryosborne.oracle-guy.com/category/oracle/plan-stability/

SQL Baselines

•Turn on with

• OPTIMIZER_USE_SQL_PLAN_BASELINE =True

• True by default

•DBA_SQL_PLAN_BASELINES

• Lists baselines that have been created

•Create with

1604/22/23

dbms_spm.load_plans_from_cursor_cache (sql_id=>'&sql_id', - plan_hashvalue=>&plan_hash_value,- fixed=>'&fixed');

SQL Baselines – Switching

1704/22/23

SQL_ID PLAN_HASH SQL_TEXT------------- ---------- ----------------------------------------------------3trqfzj8yhu6j 2709260180 select /*+ index (a col1_idx) */ avg(pk_col) from ska2h75xrkn1xh3 3498336203 select avg(pk_col) from skew a where col1 > 0

dbms_spm.load_plans_from_cursor_cache( sql_id => 'a2h75xrkn1xh3', -- Original plan_hashvalue => 3498336203 -- query);

select sql_handle from dba_sql_plan_baselines Where sql_text = 'select avg(pk_col) from kso.little_skew where col1 > 0‘;

SQL_HANDLE------------------------------SYS_SQL_6560e8852671e3e3

dbms_spm.load_plans_from_cursor_cache(- sql_id => '3trqfzj8yhu6j', -- new query plan_hashvalue => 2709260180 , -- with hint sql_handle => 'SYS_SQL_6560e8852671e3e3' /* old basline’s SQL_HANDLE */ );

http://kerryosborne.oracle-guy.com/2009/04/oracle-11g-sql-plan-management-sql-plan-baselines/

Adaptive Cursor Sharing

• Different plans for different bind variables

• Only for statements that have 14 or less variables (?!)

1804/22/23

Adaptive Cursor Sharing

select * from t1 where id < :id;

SELECT child_number, is_bind_sensitive, is_bind_aware, is_shareableFROM v$sqlWHERE sql_id = '&sql_id' ORDER BY child_number;

CHILD_NUMBER IS_BIND_SENSITIVE IS_BIND_AWARE IS_SHAREABLE------------ ----------------- ------------- ------------ 0 Y N N 1 Y Y Y 2 Y Y Y

IS_BIND_SENSITIVE - peeking used?

IS_BIND_AWARE - adaptive cursor sharing ?

IS_SHAREABLE - can be shared

1904/22/23

Adaptive Cursor Sharing

SELECT child_number, peeked, executions, rows_processed, buffer_gets

FROM v$sql_cs_statistics

WHERE sql_id = '&sql_id' ORDER BY child_number;

CHILD_NUMBER PEEKED EXECUTIONS ROWS_PROCESSED BUFFER_GETS------------ ------ ---------- -------------- ----------- 0 Y 1 19 3 1 Y 1 990 19 2 Y 1 19 3

SELECT child_number, predicate, low, high

FROM v$sql_cs_selectivity

WHERE sql_id = ‘&sql_id'

ORDER BY child_number;

CHILD_NUMBER PREDICATE LOW HIGH------------ --------- ---------- ---------- 1 <ID 0.890991 1.088989 2 <ID 0.008108 0.009910

2004/22/23

Hints

2104/22/23

All/First Rows• All_rows

• First_rows – 9i+

• First_rows_N – N in 1,10,100,1000

• First_rows(n) – n any positive number

• Only analyzes the first join order

• Get an estimate on rows returned

• Restart optimization

• First Rows

• deprecated in 9i, but maintained

• Avoid merge joins and hash joins unless alternative is nested loop with full tabelscan on inner table

• Tends to use indexed access pats

Hints - subqueries

• MERGE / NO_MERGE

• UNNEST / NO_UNNEST

• PUSH_SUBQ / NO_PUSH_SUBQ

• NO_QUERY_TRANSFORMATION

• Don’t do any of the above

2304/22/23

UNNEST

• 8i unnested nothing

• 9i unnested everything

• 10g tries to work out the cost

http://www.ardentperf.com/2007/07/18/10g-subquery-unnesting-anomalies/

UNNEST

•Choices

•NO UNNEST : Filter• scan the driving table • execute the subquery whenever necessary (a filter)

• /*+ no_unnest */

•UNNEST• create a result set with the structure (deptno, avg_sal)• join to the driving table

• /* unnest */

select outer.* from emp outerwhere outer.sal > ( select avg(inner.sal) from emp inner where inner.dept_no = outer.dept_no);

UNNEST Manual select outer.* from emp outerwhere outer.sal > ( select avg(inner.sal) from emp inner where inner.dept_no = outer.dept_no);

Select /*+ NO_MERGE */ outer.* from emp outer ( select dept_no, avg(inner.sal) avg_sal from emp group by dept_no ) innerWhere outer.dept_no = inner.dept_noand outer.sal > inner.avg_sal;

alas, if you do this in recent versions of Oracle you might then need to stop the optimizer from doing a cunning – but possibly catastrophically inefficient – piece of complex view merging by including the

/*+ no_merge */

hint in what is now the inline view (you could also achieve this through a

/*+ no_merge(inner) */

in the main query).

UNNEST

UNNEST VST

select outer.* from emp outerwhere outer.sal > ( select avg(inner.sal) from emp inner where inner.dept_no = outer.dept_no);

Emp (inner)

Emp (outer)v

v

Either execute for each roworCalculate avg(sal) for all rows as a view

PUSH_SUBQ

•Evaluate subqueries as soon as possible

• When unnest can’t be done, then subqueries are normally

evaluated at the end

PUSH_SUBQ VST

Select par.small_vc1,chi.small_vc1

From parent par,child chi

Where par.id1 between 100 and 200and chi.id1 = par.id1and exists ( select

/*+ no_unnest */null

from subtest subwhere sub.small_vc1 = par.small_vc1and sub.id1 = par.id1and sub.small_vc2 >= '2');

F F

Child (child)

Parent (par)Subtest (sub)

v

N

Subquery ParmetersParmeter 8i 9i 10g description_unnest_notexists_sq n/a single n/a Unnest not exists_unnest_subquery false true true Enable unnesting of

correlated subqueries_ordered_semi_join true true true Enable semi-join (exists)

subqueries_cost_equality_semi_join n/a true true Enable costing of equality

semi-join (exists)_always_anti_join Nested

_loopsChoose choose Always use this method for

anit-join(not exists) if pos_always_semi_join Standa

rdChoose choose A;waus ise tjos ,etjpd fpr

semi-join (exists) if pos_optimizer_correct_sq_selectivity n/a n/a true Fore correct computation of

subquery selectivity_optimizer_squ_bottomup n/a n/a true enable unnesting of

subqueries in bottom-up_distinct_view_unnesting n/a n/a false Enable unnesting of in

subqueryies into select distinct

_right_outer_hash_enable n/a n/a true Enable right out hash join

_remove_aggr_subquery n/a n/a true Eable removal of subsumed aggregate subqueries

Subquery typescorrelated/noncorrelated

Simple/complex

aggregate

Single-row

In/exists

Not in/not exists

SQL Tuning Rules

values1 field = val : SEL = (1/distinct) * nrows2 field in (val1,val2,...,valn) 8i : SEL = (1/distinct) * n * nrows - n*(1/distinct)^2 + (1/distinct)^n 9i+ : SEL = (1/distinct) * n * nrows, n <= distinct, else n=distinct3 field = val_out_of_range : SEL = (1/distinct) *nrows (wrong) 10.1.0.4+ : SEL = 1/distinct * ( 1 - max(1,distance out of range/(distinct) ) *nrows4 field > val_out_of_range : SEL = (1/distinct) *nrows5 field > val : SEL = (high-val)/(high-low)*nrows6 field >= val : SEL = (high-val)/(high-low)*nrows + 1/distinct * nrows7 field > val1 and field < val2 : SEL = (val2-val1)/(high-low)*nrows8 field >= val1 and field <= val2: SEL = (val2-val1)/(high-low)*nrows + 1/distinct * nrows + 1/distinct * nrows9 field > val1 and field < val2 : SEL = (1/distinct) *nrows 10.1.0.4+ : SEL = ((1/distinct*(1-max(1,val1 distance out of range/(distinct)) - (1/distinct*(1-max(1,val2 distance out of range/(distinct))* nrows11 field > val1 OR field < val2 : sel(val1) + sel(val2) - sel(val1 and val2)

variables1 field = :var : SEL = (.05 * nrows)2 field > :var : SEL = (.05 * nrows)3 field >= :var : SEL = (.05 * nrows)4 field like :var : SEL = (.05 * nrows)5 field > :var and field < :var : SEL = (.05 * .05 * nrows)6 field >= :var and field <= :var : SEL = (.05 * .05 * nrows)

Most Abused Parameters*

•OPTIMIZER_INDEX_CACHING

•OPTIMIZER_INDEX_COST_ADJ

•DB_FILE_MULTIBLOCK_READ_COUNT

Global band-aid for specific problems, it might help

one query and hurt others

*Greg Rahn

3304/22/23

Solutions*

•Data skew: Choose a sample size that yields accurate NDV.

Use DBMS_STATS.AUTO_SAMPLE_SIZE in 11g.

•Data correlation: Use Extended Stats in 11g. If <= 10.2.0.3 use

a CARDINALITY hint if possible.

•Out-of-range values: Gather or manually set the statistics.

•Use of functions in predicates: Use a CARDINALITY hint

where possible.

•Stats gathering strategies: Use AUTO_SAMPLE_SIZE. Adjust

only where necessary. Be mindful of tables with skewed data.

• Greg Rahn - http://structureddata.org/2007/11/21/troubleshooting-bad-execution-plans/

3404/22/23

DBA_HIST_SQLSTAT

SQL> @whats_changedEnter Days ago: 3Enter value for min_stddev:Enter value for min_etime:Enter value for faster_slower: SQL_ID EXECS AVG_ETIME_BEFORE AVG_ETIME_AFTER NORM_STDDEV RESULT------------- ------------ ---------------- --------------- ------------- ------an9114vtxukz2 17 1.25 5.00 2.1148 Slower803u6vwz0ah1p 29 0.04 0.18 2.1552 Slowerbvf3fxv3hatw7 2,390 0.03 0.14 2.4147 Slower5sgs7q9pjnzg5 2 2.21 0.42 3.0130 Fasterb0zkuv9qtcvnn 48 0.16 0.85 3.1500 Slower9ws5c6p77d384 1,852 0.57 3.30 3.3609 Slower05xcf43d9psvm 1,197 0.02 0.14 5.4263 Slower8wgmc9w5ubtsy 183 0.49 4.32 5.4946 Slowerfwfpuf1vfwfu2 6 0.02 0.22 5.6314 Slower50c18dwvxq4sb 222 0.54 5.29 6.1586 Sloweraukanfjd3d8fa 3 0.88 10.00 7.3496 Slower44bq4r5z2xrsm 54 3.13 43.39 9.0946 Slower0az7czjdw8z7j 110 0.62 0.02 17.5933 Fasterf41agfq9qdhk6 3 0.24 8.06 22.6765 Slower

3504/22/23

http://kerryosborne.oracle-guy.com/2009/06/what-did-my-new-index-mess-up/

Plan Instability

SQL> -- find statements with multiple plans with big differences in elapsed time

SQL> @unstable_plansEnter value for min_stddev:Enter value for min_etime: 1 SQL_ID SUM(EXECS) MIN_ETIME MAX_ETIME NORM_STDDEV------------- ---------- ----------- ----------- -------------f2pz10qx59awc 2 11.75 45.31 2.01975mh2127hkzbtr 70 2.64 18.06 3.02720hur96bxr18jn 24 1.65 9.14 3.198176gduk3urk91d 6 9.75 57.82 3.4880cqxkwk9hp8rpf 31 7.18 43.77 3.60153u2bxt4y0740a 17 0.49 4.19 4.1316af6j2dyzawp7w 78 6.83 60.31 4.44922mzzy3u2rtgqx 93 4.55 34.13 4.6025

3604/22/23

http://kerryosborne.oracle-guy.com/2009/06/oracle-11g-adaptive-cursor-sharing-acs/http://kerryosborne.oracle-guy.com/2008/10/unstable-plans/

Bind Variable Peeking

Solutions:•ONLY create histograms on skewed columns •USE LITERALS on histogram columns•(can use bind vars on "normal" values and litters for irregular)

•_OPTIM_PEEK_USER_BINDS = false. •Outlines/Profiles/Baselienes/Hints•11g Adaptive Cursor Sharing• JDBC 9i doesn’t bind variable peek

3704/22/23

http://kerryosborne.oracle-guy.com/2009/03/bind-variable-peeking-drives-me-nuts/

ACS - adaptive cursor sharing

•Limited to 14 variables

3804/22/23

http://kerryosborne.oracle-guy.com/2009/06/oracle-11g-adaptive-cursor-sharing-acs/

SQL_ID C# PLAN_HASH IBS IBA ISH XECS ROWS_ AVGTM SQL_TEXT------------- -- ---------- --- --- --- ---- ------ ----- ---------------0qvgb3dyfg539 1 722236007 Y Y Y 2 0 .15 SELECT row_orde17uuqnvxmzxhj 1 3038781757 Y Y Y 31 31 .17 SELECT COUNT(*) 3 3038781757 Y Y N 21 21 .02 4 3038781757 Y Y Y 52 52 .23 6 3038781757 Y Y Y 51 51 .0034x6683rpwtxa 4 722236007 Y Y Y 18 164 .01 SELECT row_orde3tfx8fzp64vkb 1 3038781757 Y Y Y 2 2 .01 SELECT COUNT(*)4vb86f36xqc50 1 2983410489 Y Y Y 62 1683 .12 SELECT row_orde 4 2983410489 Y Y Y 7 163 .69 58p0j1q6rmv34 1 1144901783 Y Y Y 2 2 .02 SELECT COUNT(*)5mxqphz5qfs4d 1 1144901783 Y Y Y 2 2 .02 SELECT COUNT(*)dt1v1cmua9cnq 1 4076066623 Y Y Y 8 37 3.47 ftxa99d89yzz0 1 4289789142 Y Y Y 2 2 .01 SELECT COUNT(*)g375mcpc30dy5 2 1690109023 Y Y N 1 10 .03 SELECT row_orde 3 1690109023 Y Y Y 5 24 .02

IBA – is bind awareIBS – is bind sensitiveISH – is shareable

More ACS

•OptimizerMagic Blog - Good basic description of ACS

OptimizerMagic Blog - Update on ACS

Ric Van Dyke - Intelligent Cusor Sharing in 11.1.0.6

Ric Van Dyke - Intelligent Cusor Sharing in 11.1.0.7

Section on ACS in Troubleshooting Oracle Performance By

Christian Antognini

3904/22/23

Same Plan Hash, different Plan

4004/22/23

http://oracle-randolf.blogspot.com/2009/07/planhashvalue-how-equal-and-stable-are_26.html