What problem are you trying to solve?

Focus on the what and why of the need you have, not the how you'd like it solved.

Currently, MongoDB supports WiredTiger (disk-backed) and the In-Memory storage engine (Enterprise only). However, there are scenarios where we want a node to process incoming writes and generate Oplog entries without retaining the actual documents in memory or on disk.

In MySQL, this is achieved via the BLACKHOLE engine. In MongoDB, a Blackhole storage engine would discard write operations immediately after updating the Oplog.

What would you like to see happen?

Describe the desired outcome or enhancement.

1. Ultra-Thin Replication Clients (An Alternative to Arbiters): Currently, when designing a replica set for high availability, an Arbiter is used to break ties in elections without holding a copy of the data. However, Arbiters do not replicate the Oplog and cannot participate in data distribution.
2. Cost-Effective Disaster Recovery (DR) in a Third Location:
3. Chained Replication Efficiency: In large geo-distributed clusters, MongoDB uses chained replication (Node B syncs from Node A, and Node C syncs from Node B) to reduce cross-region network costs.

Why is this important to you or your team?

Explain how the request adds value or solves a business need.

What steps, if any, are you taking today to manage this problem?