Re: One primary with two physical standbys exhibiting different behavior with regard to lag

Neil most likely spotted the problem. But you should also check to make sure that the protection mode is the same on both standbys.If the instance that is behind is using the maximum performance (async) mode it can run a ways behind the primary.

On Thu, Jan 3, 2019 at 3:36 PM Neil Chandler <neil_chandler_at_hotmail.com> wrote:

> Sandy,
>
> Have you checked the Standby Redo logs? There's a slight (annoying) change
> in Oracle 12.1 onwards which means that Standby Redo logs get created with
> Thread 0 instead of Thread 1 by default (for a single instance database).
> Redo can only use Standby Redo when the threads are the same. If this is
> RAC you need Standby Redo for each thread - and you must have 1 more
> Standby Redo than Online Redo for each thread.
>
> By coincidence, I wrote a blog post about this 10 minutes ago.
>
> https://chandlerdba.com/2019/01/03/data-guard-unexpected-lag/
>
> regards
>
> Neil Chandler
> Database Guy. Knows Things.
>
> ------------------------------
> *From:* oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org> on
> behalf of Sandra Becker <sbecker6925_at_gmail.com>
> *Sent:* 03 January 2019 20:29
> *To:* oracle-l
> *Subject:* One primary with two physical standbys exhibiting different
> behavior with regard to lag
>
> Oracle 12.1.0.2
> RHEL7
>
> To begin with, I have not worked much at all with standby databases, so my
> knowledge is somewhat lacking.
>
> For business reasons, we have a primary database with two physical
> standbys. Everything is configured in dgmgrl and enabled. Monitoring with
> EM13c is reporting the lag times, so all looks good for basic setup and
> monitoring. We seem to have significant lag at times on one of the
> standbys, as much as 20 minutes. When looking at v$managed_standby, we see
> the status as "WAIT_FOR_LOG". The other standby never seems to be more
> that a few seconds behind, if at all, and the status is "APPLYING_LOG".
>
> Is this normal? I've been researching, but haven't found an answer yet.
> I didn't create or start the standby databases, so I don't have any idea
> what was actually done that could be causing this behavior. Any
> suggestions would be appreciated.
>
> Thank you,
>
> --
> Sandy B.
>
>

-- 
Andrew W. Kerber

'If at first you dont succeed, dont take up skydiving.'

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