Logical initial sync adds a replica-set member by copying collection documents and indexes, recording concurrent oplog entries, and applying those entries until the member catches up. section 9.1.3
The process depends on maintaining enough oplog history:
- Copy collection documents and indexes to the new member. section 9.1.3
- Track operations generated while the initial copy runs. section 9.1.3
- Apply the recorded operations so the member reaches the primary’s current state. section 9.1.3
- Keep the oplog window long enough to prevent entries from being purged before application. section 9.1.3
Check the oplog window
Run db.getReplicationInfo() to inspect configured oplog size, usage, and the available time difference between the oldest and newest entries.
