IT04757: THE SQL OPTIMIZER PREFERS AN INDEX SCAN TO A SEQUENTIAL SCAN EVEN THOUGH IT IS 3 TIMES SLOWER

APAR status

• Closed as program error.

Error description

• If you have a large table fragmented by expression with an index
  defined on the column used for fragmentation and you run a
  simple select using that column in the WHERE clause, the
  optimizer correctly applies the fragment elimination feature but
  it chooses an index-scan path, which is 3 times slower then a
  sequential scan.
  

Local fix

• Use the optimizer directives to force the sequential scan.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * All users                                                    *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * See Error Description                                        *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * Update to IBM Informix Server 11.70                          *
  ****************************************************************
  

Problem conclusion

• Problem Fixed In IBM Informix Server 11.70
  

Temporary fix

Comments

APAR Information

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

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

Fix information

• Fixed component name

  INFORMIX SERVER

• Fixed component ID

  5725A3900

Applicable component levels

• RA10 PSN

     UP

• RA10 PSY

     UP

• RB10 PSN

     UP

• RB10 PSY

     UP

• RB50 PSN

     UP

• RB50 PSY

     UP

• RB70 PSN

     UP

• RB70 PSY

     UP

• RC10 PSN

     UP

• RC10 PSY

     UP