||Oracle Tips by Burleson
RAC Design Considerations
Proper Sequence Usage
problem with sequences is indicated in a v$system_event as an extended average wait time for row cache locks
in the range of a few hundred milliseconds. The proportion of time
waiting for row cache locks to the total time waiting for non-idle
events will be relatively high.
view, for the dc_sequences parameter, the ratio of
dlm_conflicts to dlm_requests will be high. If this ratio exceeds 10 to 15%, and the
row cache lock wait time is a significant portion of the total wait
time, then it is likely that the service time deterioration is due to
insufficiently cached sequences. For example:
SQL> col parameter format a15
SQL> select parameter, dlm_conflicts, dlm_requests, dlm_conflicts/dlm_requests ratio
2 from v$rowcache
3 where dlm_requests>0;
PARAMETER DLM_CONFLICTS DLM_REQUESTS RATIO
--------------- -------------- -------------- -----------
dc_sequences 0 2 0
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