IC98361: QUERY USING ZIGZAG IN THE ACCESS PLAN MIGHT PRODUCE WRONG RESULTS WHEN IN2JOIN IS IN THE ACCESS PLAN AS WELL.

DB2 Version 10.1 Fix Pack 4 for Linux, UNIX, and Windows
DB2 Version 10.1 Fix Pack 6 for Linux, UNIX, and Windows

APAR status

• Closed as program error.

Error description

• Queries logically similar can produce wrong result. The given
  scenario is one example
  Expected result from all the queries:-
  
  Acct  	 Acct 	 3
  2012	           2012	 71
  2013   	   2013	 20
  
  
  
  Example of incorrect results are as follows:-
  
  select test.acct, head.acct, count(*)
  from db2inst1.employee test
  join db2inst1.salary test1 on test1.rid = test.id
  where test.acct =test1.acct and test.acct in ( 2013,
  2012
  ) and test1.code = '102228'
  group by test.acct,test1.acct
  Acct 	         Acct       	 3
  2012	         2012	 71
  
  
  
  
  select test.acct,test1.acct, count(*)
  from db2inst1.employee test
  join db2inst1.salary test1 on test1.rid = test.id
  where test.acct =test1.acct and test.acct in ( 2012,
  2013
  ) and test1.code = '102228'
  group by test.acct,test1.acct
  ;
  
  Acct    	 Acct 	 3
  2013	          2013	 20
  
  Access plans will show zig zag join used with IN2JOIN in bad
  case.
  

Local fix

• Disable Zig Zag join using :-
  db2set DB2_REDUCED_OPTIMIZATION="ZZJN OFF" -IM
  

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * ALL                                                          *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * Queries logically similar can produce wrong result. The      *
  * given                                                        *
  * scenario is one example                                      *
  * Expected result from all the queries:-                       *
  *                                                              *
  * Acct       Acct      3                                       *
  * 2012               2012     71                               *
  * 2013          2013     20                                    *
  *                                                              *
  *                                                              *
  *                                                              *
  * Example of incorrect results are as follows:-                *
  *                                                              *
  * select test.acct, head.acct, count(*)                        *
  * from db2inst1.employee test                                  *
  * join db2inst1.salary test1 on test1.rid = test.id            *
  * where test.acct =test1.acct and test.acct in ( 2013,         *
  * 2012                                                         *
  * ) and test1.code = '102228'                                  *
  * group by test.acct,test1.acct                                *
  * Acct              Acct            3                          *
  * 2012             2012     71                                 *
  *                                                              *
  *                                                              *
  *                                                              *
  *                                                              *
  * select test.acct,test1.acct, count(*)                        *
  * from db2inst1.employee test                                  *
  * join db2inst1.salary test1 on test1.rid = test.id            *
  * where test.acct =test1.acct and test.acct in ( 2012,         *
  * 2013                                                         *
  * ) and test1.code = '102228'                                  *
  * group by test.acct,test1.acct                                *
  * ;                                                            *
  *                                                              *
  * Acct         Acct      3                                     *
  * 2013              2013     20                                *
  *                                                              *
  * Access plans will show zig zag join used with IN2JOIN in bad *
  * case.                                                        *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * Upgrade to DB2 Version 10.1 Fix Pack 4                       *
  ****************************************************************
  

Problem conclusion

• First fixed in Version 10.1 Fix Pack 4
  

Temporary fix

• Disable Zig Zag join using :-
  db2set DB2_REDUCED_OPTIMIZATION="ZZJN OFF" -IM
  

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

  IT16779

Fix information

• Fixed component name

  DB2 FOR LUW

• Fixed component ID

  DB2FORLUW

Applicable component levels

• RA10 PSN

     UP