-- Copyright 2018 Tanel Poder. All rights reserved. More info at http://tanelpoder.com

-- Licensed under the Apache License, Version 2.0. See LICENSE.txt for terms & conditions.

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--

-- File name: demos/bind_peeking_nested_loops.sql

-- Purpose: this script demos how a "wrong" bind variable value

-- can cause an execution plan to be compiled which is

-- very inefficient for the next execution with different bind variable

-- values (with large number of matching rows)

-- the second execution of the query takes very long time to complete

-- despite adaptive bind variable peeking, which would kick in during the

-- next (3rd) execution

--

-- This problem happens even on Oracle 11.2 despite adaptive bind peeking

-- and cardinality feedback (due design, not a bug)

--

-- Author: Tanel Poder (tanel@e2sn.com)

-- Copyright: (c) http://tech.e2sn.com

--

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DROP TABLE t1;

DROP TABLE t2;

DROP TABLE t3;

CREATE TABLE t1 AS SELECT * FROM dba_objects;

CREATE TABLE t2 AS SELECT * FROM dba_objects;

CREATE TABLE t3 AS SELECT * FROM dba_objects;

CREATE INDEX i1 ON t1(owner);

CREATE INDEX i2 ON t2(owner);

CREATE INDEX i3 ON t3(owner);

EXEC DBMS_STATS.GATHER_TABLE_STATS(user,'T1',cascade=>TRUE, method_opt=>'FOR ALL INDEXED COLUMNS SIZE 1');

EXEC DBMS_STATS.GATHER_TABLE_STATS(user,'T2',cascade=>TRUE, method_opt=>'FOR ALL INDEXED COLUMNS SIZE 1');

EXEC DBMS_STATS.GATHER_TABLE_STATS(user,'T3',cascade=>TRUE, method_opt=>'FOR ALL INDEXED COLUMNS SIZE 1');

ALTER SESSION SET OPTIMIZER_INDEX_COST_ADJ=10;

VAR v VARCHAR2(100)

EXEC :v:='SCOTT'

SET TIMING ON

PROMPT Running query first time, this should be fast (and should use nested loops execution plan)

SELECT

MIN(t1.created), MAX(t1.created)

FROM

t1

, t2

, t3

WHERE

t1.object_id = t2.object_id

AND t2.object_id = t3.object_id

AND t1.owner = :v

AND t2.owner = :v

AND t3.owner = :v

/

SET TIMING OFF

--SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(null,null,'ALLSTATS LAST ADVANCED'));

SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(null,null));

EXEC :v:='SYS'

SET TIMING ON

PROMPT Now running the same query with different bind variables (this query should take very long time)

SELECT

MIN(t1.created), MAX(t1.created)

FROM

t1

, t2

, t3

WHERE

t1.object_id = t2.object_id

AND t2.object_id = t3.object_id

AND t1.owner = :v

AND t2.owner = :v

AND t3.owner = :v

/