IT34183: POOR PERFORMANCE OF QUERIES ON SYSSCBLST PSEUDO-TABLE MAY CAUSE OTHER THREADS TO WAIT ON SESSION MUTEX

APAR status

• Closed as program error.

Error description

• Informix instances with several thousand connected sessions may
  experience poor performance of queries using the sysscblst
  pseudo-table or syssessions view in the sysmaster database.
  Statements such as "select count(*) from sysscblst" may take
  several seconds to run during which time other threads may be
  observed to wait on the session mutex. In addition advisory
  messages may appear in the online message log:
  
  Performance Advisory: Unable to get session latch.
  Results: This can happen during high connectivity periods where
  sessions are allocated and freed frequently.
  Action: This can impact session and tenant limits processing and
  low memory manager processing.
  
  The thread performing the sysscblst query may frequently be in
  the running state. The following is an example stack for the
  thread:
  
  yield_processor_mvp
  mt_unlock_helper
  mt_nxtscb
  mt_prscblst
  pstread
  pst_rsread
  rsread
  fmread
  readseq_single
  gettupl
  scan_next
  next_row
  group_open
  prepselect
  open_cursor
  sql_open
  sq_open
  sqmain
  
  In addition there may be delays in connecting new sessions or in
  the disconnection of existing sessions whilst the query is
  active.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * Users of Informix Server prior to 12.10.xC15 and 14.10.xC5.  *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * See Error Description                                        *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * Upgrade to Informix Server 12.10.xC15 (when available) or    *
  * 14.10.xC5.                                                   *
  ****************************************************************
  

Problem conclusion

• Fixed in Informix Server 12.10.xC15 and 14.10.xC5.
  

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