IT40336: PERFORMANCE PROBLEM FOR PDQ QUERY USING A SUBQUERY

APAR status

• Closed as program error.

Error description

• The fix for IT39149 "Select with PDQ and subquery can produce
  wrong results" resolves a number of issues relating to queries
  containing subqueries that run with PDQ enabled. However, this
  fix also introduces a significant performance problem such that
  the query running with PDQ may take longer than the same query
  without it.
  
  Observations of the stacks for the scan threads whilst the query
  is running show that they spend much of the time waiting on the
  "cb_anyall" mutex introduced with the fix for IT39149:
  
  yield_processor_mvp
  mt_lock_wait
  mt_lock_helper
  mt_lock
  ev_anyall
  new_eval
  gettupl
  scan_next
  producer_thread
  startup
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * Users of Informix Server prior to 12.10.xC16 and 14.10.xC8.  *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * See Error Description                                        *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * Upgrade to Informix Server 12.10.xC16 or 14.10.xC8.          *
  ****************************************************************
  

Problem conclusion

• Fixed in Informix Server 12.10.xC16 and 14.10.xC8.
  

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