Re: Redo Log problem

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 - 14:34:05 CST