Re: redologs and deadlock interaction

carab1n3r wrote:
> I'm still relatively green as a DBA, so excuse the possibly simple
> question...
>
> We have a DB that is seeing a lot of deadlocks, occasionally hundreds
> at a time. Yes, typically this is an external-application/development
> problem.
>
> However, I'm trying to determine and/or explain what impact lots-o-
> deadlocks has on redolog, particularly the switching. The reason I
> mention it is that during these "deadlock storms", we occasionally run
> out of redologs to switch to.
>
> The drumbeat I'm hearing is to "just add more redolog groups!!!" since
> that's easy to do, but we're only running into this redolog-switching
> problem during the deadlock storms, and my gut is that this is just a
> bandaid and will eventually not resolve the problem as deadlock rates
> continue to increase.
>
> So can someone explain to me (in such a way that I can explain it to
> others), when we have lots of deadlocks, what impact does that have on
> redologs?
>
>
> Thanks a lot in advance for the advice.
>

It is most likely that it is the high rate of DML activity (as seen by many log switches) that are contributing to the deadlocks. The high rate of log switches is a symptom but not a cause of your deadlocks. Log switches and redo logs do not contribute to deadlocks. If your system did not experience the high rate of DML then your chances of a deadlock would decrease.

As you said, this is an application issue. Chasing after the high rate of redo log switching is a red herring in solving your issue.

HTH,
Brian

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Brian Peasland
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