By Mike Dietrich-Oracle on Jul 01, 2015
Currently we see a lot of issues with the Multiple Logwriter feature in Oracle Database 184.108.40.206, especially on the IBM AIX platform.
What are Multiple LGWRs?
You will see multiple LGnn (Log Writer Worker) processes on multiprocessor systems, The LGWR (Log Writer) creates worker processes (slaves) to improve the performance of writing to the redo log. LGnn (Log Writer Worker) processes are not used when there is a SYNC standby destination. Possible processes include LG00-LG99.
Here is a list of new background processes in Oracle Database 12.1:
MOS Note 1625912.1 - New Background Processes In 12c
For deep dive information about how to trace the LGWR (and DBWR) and the differences 11.2/12.1 and wait events and much more, please see this Deep Dive PDF from an UKOUG talk from Frits Hoogland.
- This note has been removed without notice - I don't know the reasons ... sorry for that ...
MOS Note: 1968563.1
Hang Waiting on 'LGWR worker group ordering' with Deadlock Between LGWR (Log Writer) Slaves (LG0n) when Using Multiple LGWR Processes
- MOS Note:1957710.1
ALERT: Database hang or may fail to OPEN in 12c IBM AIX - ORA-742, DEADLOCK or ORA-600 [kcrfrgv_nextlwn_scn] ORA-600 [krr_process_read_error_2]
Turn off multiple logwriters on IBM AIX at the moment - in some cases this may solve issues on other platforms as well but please don't take this as a generic recommendation for all platforms. We are seeing the issues mainly on IBM AIX.
Set in your spfile:
- Apply Patch 21915719 or April DB PSU to prevent bug 21915719 from happening. The patch does not repair the inconsistencies in the online redo log causing the restart/open issue but prevents it from happening