Latch: redo copy (%)

Description

When a sessions redo buffer is larger than the kernel first allocates a redo copy buffer, protected by a redo copy latch.

The buffer will not be used until space is allocated on the log buffer and some header has been set. However, the redo copy latch is acquired to reduce the code inside the allocation latch holding and to prevent further contention.

Metric Summary

The rest of the information in this section is only valid for this metric when it appears in either the Enterprise Manager Grid Control or the Enterprise Manager Database Control (if applicable).

The following table shows how often the metric's value is collected and compared against the default thresholds. The 'Consecutive Number of Occurrences Preceding Notification' column indicates the consecutive number of times the comparison against thresholds should hold TRUE before an alert is generated.

Target Version	Evaluation and Collection Frequency	Upload Frequency	Operator	Default Warning Threshold	Default Critical Threshold	Consecutive Number of Occurrences Preceding Notification	Alert Text
pre-10g	Every Minute	After Every Sample	>	20	Not Defined	3	%value%%% of service time is spent waiting on the 'latch: redo copy' event.

Data Source

(DeltaLatchRedoCopyTime/DeltaServiceTime)*100 where:

DeltaLatchRedoCopyTime: difference of 'sum of time waited for sessions of foreground processes on the 'latch: redo copy' event' between sample end and start
DeltaServiceTime: difference of 'sum of time waited for sessions of foreground processes on events not in IdleEvents + sum of 'CPU used when call started' for sessions of foreground processes' between sample end and start

See Idle Events

User Action

The number of redo copy latches is controlled by the init.ora . If the parameter is not set, it defaults to the number of CPUs.

For log generating processes, the latch get is made in an immediate mode, then it will be convenient to have enough redo copy latches to reduce contention of foreground processes.

Before flushing out the log buffer, the LGWR will acquire all redo copy latches in a willing-to-wait mode. Thus an excessive number of copy latches will cause contention in the log buffer flushing process.

The number of LWGR redo copy latch allocations is redo writes * No.redo copy latches.

Related Topics

About Alerts

About the Metric Detail Page

Editing Thresholds

Understanding Line Charts

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