Mongodb – Consequences of increase Oplog to large size


I'm trying to add a new member (m*-server: 4.2.7) in my replica set (m*-servers: 4.2.1),
and it can't sync in time, after the initial sync it changes state to RECOVERING and have: (~ 4.3 - 6.31 hrs) behind the primary; Oplog size: "usedMB" : 50769.34, "timeDiffHours" : 1.19 ( ~0.79 -1.19).

I can't optimize queries or reduce size of dbs (~1.9T), or make backup and copy data (there is not enough time),
so think only solution for me is replSetResizeOplog on all members.

What the consequences can be I if increase size of Oplog larger than Upper Bound: 50GB (WiredTiger Storage Engine) to for example: 400 Gb?

Best Answer

Nothing negative, if you don't count the usage of disk space. Actually you need just make your Primary nodes OpLog bigger and then wait at least that 6 hours to fill it enough. But of course it's good to have same size OpLog on every RS node. I try to keep OpLog size at least 48h. That gives you "time" to solve problems, if those rise up.