Re: Database file configuration for backup/recovery

Recovery time is a combination of the amount of redo to be read, and the number of buffers to be recovered. The log_checkpoint parameters only affect the first of those. You could imagine, for example, a transaction which does expensive inserts and deletes, thus generating reams of redo, but which happened only to affect one or two buffers. Lots of redo to be read, few buffers to be recovered. Conversely, a bunch of updates might generate piddly amounts of redo, but dirty hundreds of buffers (each of which then has to be read from disk on subsequent startup, thus generating stacks of *datafile* I/O).

You need to set FAST_START_IO_TARGET to limit the number of buffers effectively. The_interval and _io_target parameters in tandem do a pretty good job of limiting recovery time.

Regards
HJR

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"Keith Boulton" <kboulton_at_ntlworld.com> wrote in message
news:IOxe8.4144$R16.741296_at_news11-gui.server.ntli.net...


>

> Keith Boulton <kboulton_at_ntlworld.com> wrote in message

> news:V24e8.28567$hM6.3678545_at_news6-win.server.ntlworld.com...

> > failure than in the last 2 hours, so I would go for a checkpoint timeout

> in

> > that case.

> >

> Doh!

>

> Of course, as someone else pointed out, checkpoint timeout is irrelevant

to


> this discussion.

>

> I do, however, have a question.

>

> Has anyone actually tested the impact of these parameters on recovery

time?


>

> As I said, I have in the past attempted to find a penalty associated with

> larger logs, but always with checkpoint interval set high and checkpoint

> timeout set to 0. While I'm happy enough to believe that my testing

matches


> by theorising about limiting factors affecting restart time, I can't help

> wondering if there's something I've missed.

>

> Any suggestions?

>

>