That's true, if you use the the CAP definition for consistency. Otherwise, I'd say that the DNS design satisfies each of those terms:
- "Rapidly updatable" depends on the specific implementation, but the design allows for 2 billion changesets in flight before mirrors fall irreparably out of sync with the master database, and the DNS specs include all components necessary for rapid updates: push-based notifications and incremental transfers.
- DNS is designed to be eventually consistent, and each replica is expected to always offer internally consistent data. It's certainly possible for two mirrors to respond with different responses to the same query, but eventual consistency does not preclude that.
- Distributed: the DNS system certainly is a distributed database, if fact it was specifically designed to allow for replication across organization boundaries -- something that very few other distributed systems offer. What DNS does not offer is multi-master operation, but neither do e.g. Postgres or MSSQL.
That's true, if you use the the CAP definition for consistency. Otherwise, I'd say that the DNS design satisfies each of those terms:
- "Rapidly updatable" depends on the specific implementation, but the design allows for 2 billion changesets in flight before mirrors fall irreparably out of sync with the master database, and the DNS specs include all components necessary for rapid updates: push-based notifications and incremental transfers.
- DNS is designed to be eventually consistent, and each replica is expected to always offer internally consistent data. It's certainly possible for two mirrors to respond with different responses to the same query, but eventual consistency does not preclude that.
- Distributed: the DNS system certainly is a distributed database, if fact it was specifically designed to allow for replication across organization boundaries -- something that very few other distributed systems offer. What DNS does not offer is multi-master operation, but neither do e.g. Postgres or MSSQL.
I think historically DNS was “best effort” but with consensus algorithms like raft, I can imagine a DNS that is perfectly consistent