85 lines
2.4 KiB
SQL
85 lines
2.4 KiB
SQL
--------------------------------------------------------------------------------
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--
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-- File name: demos/bind_peeking_nested_loops.sql
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-- Purpose: this script demos how a "wrong" bind variable value
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-- can cause an execution plan to be compiled which is
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-- very inefficient for the next execution with different bind variable
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-- values (with large number of matching rows)
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-- the second execution of the query takes very long time to complete
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-- despite adaptive bind variable peeking, which would kick in during the
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-- next (3rd) execution
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--
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-- This problem happens even on Oracle 11.2 despite adaptive bind peeking
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-- and cardinality feedback (due design, not a bug)
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--
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-- Author: Tanel Poder (tanel@e2sn.com)
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-- Copyright: (c) http://tech.e2sn.com
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--
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--------------------------------------------------------------------------------
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DROP TABLE t1;
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DROP TABLE t2;
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DROP TABLE t3;
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CREATE TABLE t1 AS SELECT * FROM dba_objects;
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CREATE TABLE t2 AS SELECT * FROM dba_objects;
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CREATE TABLE t3 AS SELECT * FROM dba_objects;
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CREATE INDEX i1 ON t1(owner);
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CREATE INDEX i2 ON t2(owner);
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CREATE INDEX i3 ON t3(owner);
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EXEC DBMS_STATS.GATHER_TABLE_STATS(user,'T1',cascade=>TRUE, method_opt=>'FOR ALL INDEXED COLUMNS SIZE 254');
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EXEC DBMS_STATS.GATHER_TABLE_STATS(user,'T2',cascade=>TRUE, method_opt=>'FOR ALL INDEXED COLUMNS SIZE 254');
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EXEC DBMS_STATS.GATHER_TABLE_STATS(user,'T3',cascade=>TRUE, method_opt=>'FOR ALL INDEXED COLUMNS SIZE 254');
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ALTER SESSION SET OPTIMIZER_INDEX_COST_ADJ=10;
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VAR v VARCHAR2(100)
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EXEC :v:='SCOTT'
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SET TIMING ON
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PROMPT Running query first time, this should be fast (and should use nested loops execution plan)
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SELECT
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MIN(t1.created), MAX(t1.created)
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FROM
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t1
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, t2
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, t3
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WHERE
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t1.object_id = t2.object_id
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AND t2.object_id = t3.object_id
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AND t1.owner = :v
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AND t2.owner = :v
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AND t3.owner = :v
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/
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SET TIMING OFF
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--SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(null,null,'ALLSTATS LAST ADVANCED'));
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SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(null,null));
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EXEC :v:='SYS'
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SET TIMING ON
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PROMPT Now running the same query with different bind variables (this query should take very long time)
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SELECT
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MIN(t1.created), MAX(t1.created)
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FROM
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t1
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, t2
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, t3
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WHERE
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t1.object_id = t2.object_id
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AND t2.object_id = t3.object_id
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AND t1.owner = :v
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AND t2.owner = :v
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AND t3.owner = :v
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/
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