In case of heavy contention for latches, set the LOG_SIMULTANEOUS_COPIES initialization parameter to
Twice the number of CPUs
1. What is meant by "Heavy contention of latches"
2. What is the use of of the parameter LOG_SIMULTANEOUS_COPIES
LOG_SIMULTANEOUS_COPIES specifies the maximum number of redo buffer copy latches available to write log entries simultaneously. For good performance, you can have up to twice as many redo copy latches as CPUs. For a single-processor system, set to zero so that all log entries are copied on the redo allocation latch
In Oracle,if a process wants to write anything into the SGA it has to acquire a latch.So if LGWR wants to write to redo log files it has to acquire a latch so that no other process makes changes to that part when it is copying.
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Rohit Nirkhe,Oracle DBA,OCP 8i
Thanks Rhit. Will you please explain the term Latches..? Is it buffers itself?
Hi, 25th April 2001 13:28 hrs chennai
Latches are not buffers.It is a used to protect access to internal structures.
A process which needs to change this structures first need latches to acuire.
latches are held by them till it has finished its task.
Most cases of latch contention occur when two or more process concurrently attempt to btain the same latch.This rarely occurs on a single CPU computers where only single process can be active at once.
You can use v$latch and v$latchname to query the statistics.
The LOG_SIMULTANEOUS_COPIES should be always twice the number of CPU's
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