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@xxxxxxxxxxx>
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@xxxxxxxxxxxxx <oracle-l-bounce@xxxxxxxxxxxxx> on
behalf of Sandra Becker <sbecker6925@xxxxxxxxx>
*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.
