IT22630: Performance Regression might be Observed with Queries ContainingNOT EXISTS or NOT IN Predicates

Db2 Version 11.1 Mod 3 Fix Pack 3 for Linux, UNIX, and Windows
Db2 Version 11.1 Mod3 Fix Pack3 iFix001 for Linux, UNIX, and Windows
Db2 Version 11.1 Mod3 Fix Pack3 iFix002 for Linux, UNIX, and Windows

APAR status

• Closed as program error.

Error description

• Users might observe performance regression when upgrading from
  V9.7 and running queries with the following characteristics:
  1. Queries contain NOT EXISTS or NOT IN predicates
  2. Sub-queries in the NOT EXISTS or NOT IN predicates contain
  correlated sub-queries
  3. The correlation sources of these correlated sub-queries are
  local to the NOT EXISTS or NOT IN sub-queries
  
  An example of such a query is:
  
  select p1
  from   p
  where not exists
  (select *
  -- This NOT EXISTS sub-query contains correlated sub-queries
  from (select *
         from a
        where exists (select 1                              --
  This correlated sub-query has correlation source from Table A
  which is local to the NOT EXISTS sub-query
                             from b
                             where b1=a1 order by b1)
        fetch first 1 row only) q
  where q.a2 = p.p1)
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * ALL                                                          *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * See Error Description                                        *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * Upgrade to Db2 11.1 Mod 3 Fix Pack 3 or higher               *
  ****************************************************************
  

Problem conclusion

• First fixed in Db2 11.1 Mod 3 Fix Pack 3
  

Temporary fix

Comments

APAR Information

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

  IT20659

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

Fix information

• Fixed component name

  DB2 FOR LUW

• Fixed component ID

  DB2FORLUW

Applicable component levels

• RB10 PSN

     UP