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Re: log buffer question

From: Connor McDonald <connor_mcdonald_at_yahoo.com>
Date: Thu, 16 Aug 2001 18:12:17 +0100
Message-ID: <3B7BFEF1.50A6@yahoo.com>


Zin Zean wrote:
>
> Hello.
> I'm running 8.1.7 on Solaris 2.7. My database supports a web site.
>
> When oracle writes to the redo log file, such as when a user performs a
> commit,
> does it write LOG_BUFFER (setting in the init.ora) number of bytes? ie.
> flush the entire log buffer?
>
> Or does it only write transaction's redo buffer information?
>
> The reason I'm asking is that the top two wait events in our system is
> log file sync and log file parallel writes. Since these two events have
> waits
> on the same order of magnitude I'm assuming that we're writing to the
> redo log at a high rate b/c of the number of commits in our system.
> And we have LOG_BUFFER set to 512K and our redos at 10M we are
> seeing 100's of log switches in an hour. And I'm hoping that if we
> reduce LOG_BUFFER the log switch frequency will go down.
>
> Thanks.

"All" of the log buffer is flushed out where "all" is whats currently used (which
may be more than what the current txn has written into it). 100's of switches
per hour sounds like an awful lot - I'd look at bumping your logs up to 500M or
so.

Other than that, the normal stuff applies - isolate the disks that they are on, make
them raw devices to enable async writes, try reduce the commit frequency etc.

hth
connor

-- 
==============================
Connor McDonald

http://www.oracledba.co.uk

"Some days you're the pigeon, some days you're the statue..."
Received on Thu Aug 16 2001 - 12:12:17 CDT

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