'redo synch time overhead ...' statistics

  • From: "Chitale, Hemant K" <Hemant-K.Chitale@xxxxxx>
  • To: ORACLE-L <oracle-l@xxxxxxxxxxxxx>
  • Date: Thu, 3 Dec 2015 03:28:57 +0000

Apparently, v$sysstat does have statistics like

redo synch time (usec)
redo synch time overhead (usec)
redo synch time overhead count (<128 msec)
redo synch time overhead count (<2 msec)
redo synch time overhead count (<32 msec)
redo synch time overhead count (<8 msec)
redo synch time overhead count (>=128 msec)



Oracle Support note "Bug 12614085 - Diagnostic enhancement to add new
statistics for investigating "log file sync" and "log file parallel write"
relationship (Doc ID 12614085.8)" talks of an enhancement that enables this
collection but I am not sure I understand it.

Can anyone interpret that note and help me understand that statistics ? If I
see the overhead time being reported by these statistics, what really (what
overhead) does it represent ? What if we have DataGuard in the picture ? Does
it also reflect DataGuard LGWR SYNC overheads ?


Hemant K Chitale





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