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An impact report from the front-lines of nostr client development.
Negentropy
NIP-77, Negentropy Syncing
A set reconciliation protocol for finding which records each side is missing without exchanging every ID.
Negentropy is a set reconciliation protocol. It lets two sides compare large sets efficiently, learn which entries one side has that the other side is missing, and then transfer only the missing records. Nostr uses it to sync events between clients and relays.
In Nostr, NIP-77 brings Negentropy into the protocol so a client and relay can compare the events they have for a chosen filter and sync whatever is missing.
This reduces bandwidth when both sides already share much of the same history. It is useful for client-relay sync and relay-relay sync.