Re: 'redo synch time overhead ...' statistics

> Can anyone interpret that note and help me understand that statistics ?

Oracle Patent #US20140258223-A1 got an explanation of it. Just quoting from it: "Redo synchronization time and overhead. The latency observed by the process committing the transaction. It is the sum of how long it takes the log writing process to receive the log write request, the redo log write time, and the redo synchronization overhead. The overhead is the time between the completion of the log write and the time at which the committing process detects that the log write is done, and consequently reflects the latency added by post-wait or poll-wait. Thus, the ideal redo synchronization time is the redo synchronization time minus the overhead."

More internals about post-wait or poll-wait mechanism can also be found in Frit's slides (21 to 23): https://fritshoogland.files.wordpress.com/2015/09/profiling-the-logwriter-and-database-writer.pdf

Best Regards
Stefan Koehler

Freelance Oracle performance consultant and researcher Homepage: http://www.soocs.de
Twitter: _at_OracleSK  

> "Chitale, Hemant K" <Hemant-K.Chitale_at_sc.com> hat am 3. Dezember 2015 um 04:28 geschrieben:
>
> 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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