Re: Increase in 'log file sync' waits while 'log file parallel write' remains unchanged

From: joel garry <>
Date: Tue, 22 Sep 2009 10:23:30 -0700 (PDT)
Message-ID: <>

On Sep 21, 5:14 pm, John Hurley <> wrote:
> On Sep 21, 8:02 pm, John Hurley <> wrote:
> snip
> > Most of my systems are at 128 MB ... why would you have a system with
> > a 1 MB log buffer?
> Missed ... looks like my systems are at 10 MB log_buffer not sure why
> 128 jumped into my mind.
> The old advice for 1MB is afaik not relevant much anymore.  Several
> metalink articles available if you search log_buffer ...

Pehaps you've forgotten that Oracle rounds up log buffer to fill up a granule on 10gR2 and up. Perhaps at some point you set a 65M log_buffer and found it at 128. Perhaps you're running apps and that's what was recommended before 10gR2.

Here's a forum thread that explains some stuff, including that a toobig  buffer may cause log syncs:

Of course, I don't expect that 1M is too big. I'd guess that something is happening on the OS side periodically that is pounding I/ O (or like you suggested, cpu starvation is preventing I/O from happening, but...). The waits aren't on parallel write perhaps because it's being written to a hardware cache, but the commit ack isn't coming back. Would there be snaps happening on the SAN? Why does this sound so familiar, like an async i/o problem? Which AIX is this? Search metalink for async i/o ibm, see things like Note: 233659.1


-- is bogus.
Received on Tue Sep 22 2009 - 12:23:30 CDT

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