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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 missing records without sending every ID.
Negentropy is a set reconciliation protocol. It helps two sides figure out which records are missing on each side, so they can transfer only those records. When both sides already share many records, this uses less bandwidth than sending the full set of records or even a full list of IDs. Nostr uses it to sync events between clients and relays.
In Nostr, NIP-77 wraps Negentropy so a client and relay can compare the events they have for a chosen filter and sync what is missing.
It works for client-relay sync and relay-relay sync.