SYMPTOMS
Entries such as the following lines appearing in FairCom DB's status log file CTSTATUS.FCS:
WARNING: ct_lflsema livelock
Log flush from buffer overflow. Current LFW Channel block not set: 1
CAUSE
This condition occurs when the COMMIT_DELAY logic is enabled and FairCom DB is trying to acquire a lock on the log flush semaphore (ct_lflsema). If a large number of retries does not lead to either acquisition of the semaphore or the flushing of the log, then a warning is posted in the status log about a possible livelock problem, and the commit delay logic is automatically disabled. The consequence of disabling the commit delay logic could lead to a drop of performance.
A possible condition that may trigger a "ct_lflsema livelock" warning, may occur during a log extension operation of a large transaction log files (L*.FCS). If the operation takes too long to complete, it may cause an excessive looping that in turn produces the warning situation.
RESOLUTION
If the cause of the warning is latency during log extension, you have a number of options to decrease the latency:
MORE INFORMATION
It is impossible to know if a livelock detection represents a deadlock scenario, or simply a timing issue that would have cleared if the limit on the retry loop counter was increased. The limit is set by a #define and increasing such value requires a customization of FairCom DB.
For additional information about the Transaction Log Template feature, please read the Transaction Log Template White Paper.
