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

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.

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,

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Sandy B.

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http://www.freelists.org/webpage/oracle-l Received on Thu Jan 03 2019 - 22:34:45 CET