Re: Redo Log problem

I have been running 2GB redo logs ( only 2 of them ) on a development instance for performance boost for long running, heavy insert/update transactions. Before going to 512M, then 1024M, then 1500M and finally 2GB, performance was good. But with the 2GB logs, this instance is a screamer. At the peak of activity, this thing will still switch logs ( and checkpoint ) about once every 10 minutes. The 100 fold ( or so ) increase in performance over a 105MB log size was certainly worth whatever trade-off I incurred.

As for recovery, if this thing were to fail during this processing, I'd have much larger problems to deal with.

-Kevin

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Chuck Hamilton wrote in message <3634d7d3.16093099_at_news2.axs2000.net>...
>On Wed, 21 Oct 1998 20:24:19 -0700, Jeremiah Wilton
><jeremiah_at_wolfenet.com> wrote:
>
>>Remember that with less frequent checkpointing, you may incur several
>>detrimental effects:
>>
>>- You will experience increased mean time to recovery (MTR) for crash
>> recovery, because crash recovery has to start application of redologs
>> from the point in time of the most recent checkpoint. The longer ago
>> that was, the more recovery you will have to do.
>>
>>- You will notice an increased incidence of "busy buffer" waits and "write
>> complete" waits for sessions, because more buffers in the block buffer
>> cache are dirty at any given time.
>>
>>- It will increase the number of dirty buffers that must be written out
>> for a checkpoint, making the checkpoint take longer.
>
>Which do you think is worse:
>
>1) busy buffer waits, or
>2) writing every dirty buffer to disk, *and* updating the
> header of every datafile in the database, and archiving
> a log file (if archivelog mode is employed).
>
>I'd gladly take #1 over #2.
>
>The point about MTR is well taken, but in all honesty, how often do
>you need to recover a database? I think that minute to minute
>performance is more important than the once or twice a year that you
>may need to perform recovery.
>
>Most of the recoveries we've had to do were done with the online logs.
>We use 1G (that's no type-o) log files on our data warehouse and
>recovery from online logs never takes more than about 15 minutes.
>
>--
>Chuck Hamilton
>chuckh_at_safeaccess.net
>
>If at first you don't succeed, sky diving isn't for you.
Received on Mon Oct 26 1998 - 15:00:34 CST