Hello,

We are running mongodb replica set.

I have a question about oplog's size , by default it's 5% of the disk size .

What happens when oplog size is full ? Will overwrite old data ? 

I'm asking because of point-in-time recovery backup . 

For example i would have oplog backup for 2 weeks retention  , so i dont want to have oplog file from december 2019 ,but only from 1st january 2020 .  What should be done in this case ?