System Type: Peer-to-Peer (P2P)

Patterns, failure modes, and anti-patterns for decentralized peer-to-peer systems.

Network Topologies

Unstructured (Gossip / Flood)

When to use. Systems where any peer can hold any data and queries are exploratory — file sharing (early Gnutella), social feeds, informal mesh networks. When simplicity and resilience to churn matter more than lookup efficiency. When to avoid. Systems that need efficient key-based lookups. Large networks where flooding creates unacceptable bandwidth overhead. When query latency must be predictable. Key decisions. TTL (time-to-live) on forwarded messages, fanout degree (how many peers each node forwards to), duplicate message suppression, supernode election for partial structure.

Structured (DHT)

When to use. Efficient key-value lookups in a decentralized network — content-addressable storage, distributed hash tables (Kademlia, Chord, Pastry). When you need O(log n) lookups instead of flooding. When to avoid. When keyword search or range queries are needed (DHTs only do exact key lookup). When the network has extremely high churn (DHT routing tables become stale faster than they can repair). Very small networks where the DHT overhead exceeds the benefit. Key decisions. Hash function and key space design, replication factor (k-bucket size in Kademlia), routing table refresh strategy, handling network partitions and merges, iterative vs recursive lookup.