Replication is how Notes and Domino keep copies of a database synchronised between servers and clients, so users can work offline and data exists in several places.
Replication is how Notes and Domino keep copies of a database synchronised. An NSF database can exist on several servers and on users' PCs, and replication makes sure changes flow between all copies. It was Notes' great invention in 1989 and is still one of the platform's biggest strengths.
How does replication work?
Every database has a replica ID. Two databases with the same ID are copies of each other. When replication runs, the documents are compared, and the latest changes are copied both ways. Only changed fields are sent, so it is fast even over slow connections. Replication between servers is controlled by connection documents in Domino Directory, typically every 15 to 60 minutes. Clients replicate when the user opens Notes, or on a schedule.
What is it used for?
- Offline work: Sales staff and technicians work in a local copy and synchronise when they are back online.
- Redundancy: The same database on two servers. If one goes down, clients use the other.
- Geography: Offices in several countries each have their own server with local copies.
- Backup: A replica in another data centre is a running copy.
Replication conflicts
If two users change the same document in separate copies before replication has run, a conflict arises. Notes keeps both versions and marks one as a conflict document. Many old applications have hundreds of conflicts nobody has cleaned up. That is part of ordinary maintenance.
Typical faults
- Replication has stopped, because one server lacks access in the other's ACL.
- An old replica on a forgotten server sends outdated documents back.
- Deleted documents reappear, because deletion stubs have expired.
All three are caught with server monitoring.
Common questions
Is replication the same as backup?
No. An error replicates too. You still need real backup.
Does replication exist in Microsoft 365?
Not in the same way. It is one of the things that makes migration of offline applications hard.
Does replication work in Nomad?
Yes. Nomad Mobile can keep local replicas on the phone.