Increase oplog size in replicaset

[roberto cirillo]

Hi all,

 In an existing Replica set (1 primary 2 secondaries) I need to increase the oplog size from 5GB to 10 GB. I've found in the official documentation a procedure to do it: https://docs.mongodb.com/manual/tutorial/change-oplog-size/

Are really needed all these steps? Or it could be simplified  with the following steps for every secondary member:

- stop the secondary member,

- increase oplog size;

-restart the secondary member.

and for primary:

- stepDown

- repeat the secondary's procedure

Thanks in advance

Roberto

[William Hagan]

Hi Roberto,

You will need to be connected to the running mongod instance of the secondary in order to change the oplog size as such, the instance will have to be restarted in standalone mode and on a different port to prevent other replica set members from communicating with it.

Also, being that the oplog is a capped collection, it can only be recreated and not modified.

So, I think the steps highlighted in the docs are necessary - except of course backing up the existing oplog collection.

Cheers

[roberto cirillo]

Thank you William for your reply.

So,  if I need to do a full resynch on a secondary member (deleting all the data). Could I just increase the oplog size before start the resynch?

I assume, with a full resynch, the oplog collection is re-created from scratch.

Cheers

[William Hagan]

Yes, before the secondary rejoins the replica set, you should set the oplog size.

A resync wouldn't recreate the oplog collection from scratch.

Cheers.

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