IT38498: ONMODE -C BLOCK ON RSS FAILS TO FULLY BLOCK LEAVING MREPLAY THREAD IN COND WAIT RESUME_APP - NO MORE LOG APPLY UNTIL RESTART

APAR status

• Closed as program error.

Error description

• When running onmode -c block or using the API (as below) on an
  RSS:
  
  echo "execute function task ('checkpoint','block');" | dbaccess
  sysadmin
  
  The instance may fail to fully block, leaving the instance
  unable to be unblocked via onmode -c unblock or the api
  equivalent:
  
  echo "execute function task ('checkpoint','unblock');" |
  dbaccess sysadmin
  
  The main symptoms are:
  
  1, The online.log does not report "Dynamic Server Blocked" as
  would be expected.
  
  Below is from a successful block:
  
  11:14:06  SCHAPI: Issued Task() or Admin() command "task(
  'checkpoint', 'block' )".
  11:14:06  SCHAPI: Issued command "onmode". This is the only
  record of the command issuance.
  11:14:09  Logical Log 4712 Complete, timestamp: 0x16123736.
  11:14:09  Staging of logical logs successfully started.
  11:14:09  Checkpoint Completed:  duration was 0 seconds.
  11:14:09  Fri Sep 24 - loguniq 4713, logpos 0x7c1018, timestamp:
  0x16129efc Interval: 21098
  
  11:14:09  Maximum server connections 1
  11:14:09  Checkpoint Statistics - Avg. Txn Block Time 0.000, #
  Txns blocked 0, Plog used 151, Llog used 0
  
  11:14:10  The external backup is blocking the database server at
  checkpoint 4713:0x7c1018.
  11:14:10  External Backup preparation complete - Time 3.027
  11:14:10  Dynamic Server blocked.
  
  2. The mreplay thread remains in the following cond wait state:
  
   115      4ac62368         45e8a9e8         3    cond wait
  RESUME_app   8cpu         mreplay
  

Local fix

• Reducing the number of OFF_RECVRY_THREADS to lower values may
  reduce the occurrence, but this has to be considered in
  conjunction with:
  VPCLASS cpu,num=N
  SEC_APPLY_POLLTIME=N - this should be 100 or lower but testing
  should be performed to ensure Log Replay Apply performance is
  not deteriorated
  OFF_RECVRY_THREADS N - this should be lowered to values between
  10 and 20 but testing should be performed to ensure performance
  is not deteriorated
  

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * Users of Informix Server prior to 14.10.xC7.                 *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * See Error Description                                        *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * Upgrade to Informix Server 14.10.xC7.                        *
  ****************************************************************
  

Problem conclusion

• Fixed in Informix Server 14.10.xC7.
  

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