Re: Redo Copy Latches

From: Steve Adams <steveadams_at_acslink.net.au>
Date: 1997/11/03
Message-ID: <345d2b0f.11491968@newsserver.trl.oz.au>#1/1

Hi Raju,

I think the answer is that as of 7.3 for any redo entry, a copy latch is requested in immediate mode initially and if obtained the allocation latch is released, otherwise the allocation latch is held and the copy proceeds on the allocation latch. When the copy has finished the latch is released, which may be either an allocation or a copy latch,

In earlier versions, it worked the other way: a copy latch was obtained first, and then the allocation latch (unless the entry was less than the small entry threshold, of course).

I think there is an exception when an entry is copied in multiple copy calls, rather than just one. In this case, I think, a willing-to-wait get on the copy latch occurs for each subsequent copy. However, that does not explain the relatively poor hit rate that one observes on such gets, so there must be something more to it than I have so far worked out.

Any help appreciated ...

Thanks,
Steve Adams
steveadams_at_acslink.net.au

---

On Fri, 31 Oct 1997 16:16:37 -0800, Raju Krishnamoorthy <rajuk_at_corp.sgi.com> wrote:

>Does anyone know when a redo copy latch is acquired in a wait mode and
>when under immediate (no wait) mode ?
>
>Thanks
>Raju
Received on Mon Nov 03 1997 - 00:00:00 CST