RE: Way to much log switching!!!

Jeremiah, we still run version 9 and do not use Fast Start Fault Recovery but from the version 10g Concepts manual notice this little blurb: "Fast-start checkpointing eliminates bulk writes and the resultant I/O spikes that occur with conventional checkpointing." This would seem to indicate that rapid log switches could result in DBWR IO problems, which I have in fact seen in earlier versions. With 10g you may want to choose sizing based on different considerations since this should no longer be an issue, but I still see no valid reason to switch logs every two minutes except maybe under peak levels.

• Mark D Powell --

-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org]On Behalf Of Jeremiah Wilton Sent: Wednesday, June 30, 2004 4:10 PM
To: 'oracle-l_at_freelists.org'
Subject: RE: Way to much log switching!!!

On Wed, 30 Jun 2004, Powell, Mark D wrote:

> I for one like my online logs sized such that in 24 hours the db generates
> 24 to 48 logs. This is a reasonable number of logs to work with if you
ever
> have to perform manual roll forward during recovery. This might be the
case
> where you do not have enough room to keep all the uncompressed logs since
> the last backup on disk in one location. Then there is that little
feature
> where checkpoints are triggered on a log switch and all dirty blocks are
> written to disk. I see no reason to force buffer flushing this
frequently.

In modern Oracle, checkpoints happen constantly as part of the fast start mechanism. In 10g this is the default. Even in the days of log_checkpoint_interval, the only stuff written to disk was what was on the LRUW list, not the whole buffer cache!

So I don't buy that frequent checkpoints adversely affect the cache or performance. Checkpoints only use a small portion of the DBW0's write batch anyway.

As for recovery, why is it more difficult to recover with 100 32M logfiles than with 10 320M logfiles? I use wildcards to copy stuff and automatic log apply to roll forward. I could even argue that in the case of a restore, the first 32M logfile is going to be restored sooner than the first 320M log, allowing me to commence roll forward sooner, and shorten overall time to recover.

--
Jeremiah Wilton
http://www.speakeasy.net/~jwilton



> -----Original Message-----

> From: oracle-l-bounce_at_freelists.org

> [mailto:oracle-l-bounce_at_freelists.org]On Behalf Of Jeremiah Wilton

>


> On Wed, 30 Jun 2004, Mark Moynahan wrote:

>
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