How to detect Replication failures (if any) in MongoDB?

[Karthik Bhat]

How to detect Replication failures between primary and secondary nodes in mongo (if any)? Can you please point me to the documentation?

[Nikhil R]

Replication failures generally happens when the Primary node is down and the members of replica sets takes around 10-30 secs to acknowledge the in accessibility of the Primary node.

Then, the members of replica sets will hold an election to select the Primary node. This is when the MongoDB will not be available for writes. 

So the total time taken for the entire process above is around 1 min.

You can get this info in the mongodb logs of the nodes.

-Nikhil

[Asya Kamsky]

What exactly do you mean by replication failures? MongoDB
replication is designed in such a way that if a secondary fails to
successfully apply an operation from the primary it will NOT continue
- it will try again or throw a fatal error.

So you will see it in the logs if a secondary had a failure
replicating from a functioning primary.

If you meant something else by replication failure, could you clear up
what exactly you're thinking of?

Asya

On Tue, Aug 25, 2015 at 10:31 PM, Karthik Bhat <karthi...@gmail.com> wrote:
> How to detect Replication failures between primary and secondary nodes in
> mongo (if any)? Can you please point me to the documentation?
>

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[Karthik Bhat]

Thank you Asya. I wanted to check if an entry in oplog will be skipped if replication fails for that entry. If it keeps trying then that's great. If mongo were to throw a fatal error how would the log line look like? Can you please paste a log entry if that case were to happen?

[Asya Kamsky]

> fatal error how would the log line look like? Can you
> please paste a log entry if that case were to happen?

I'm afraid I can't do that, there is not a single possible error,
there can be many.

Asya

> https://groups.google.com/d/msgid/mongodb-user/a9831061-b2ee-4008-99c6-679f36bfcf78%40googlegroups.com.