CONCEPT Cited by 1 source
Split-brain¶
Split-brain is the failure mode in which two (or more) nodes each believe they have authoritative ownership of the same resource — typically a key, partition, or leadership role. Or the dual: no node thinks it owns the resource, and requests drop silently. Both shapes appear under partition/crash/intermittent-failure scenarios when ownership is decided without a coordinator.
Where it shows up in sharding¶
Static-sharding schemes compute key → node independently in each client (concepts/static-sharding). When pods crash or become intermittently unresponsive, clients can arrive at inconsistent views of membership:
- Two pods own the same key → writes may conflict or be silently lost; cache coherence breaks.
- No pod owns the key → customer traffic is dropped entirely.
Static consistent-hashing has no pathway to prevent either outcome because there's no authoritative record of "who owns what right now" — just whichever clients each client sees as alive.
Mitigations¶
- Central coordinator (the dynamic-sharding posture of systems/dicer / systems/slicer / systems/shard-manager): assignment is state published by one authority; clients converge on it.
- Leases (systems/centrifuge / systems/slicer): ownership is a time-bounded lease issued by the coordinator; a pod without a valid lease does not serve.
- Consensus-based leadership (Raft / Paxos / ZooKeeper): strongest form; the overhead that "soft" leader election (concepts/soft-leader-election) deliberately avoids.
Trade-off with eventual consistency¶
systems/dicer chose concepts/eventual-consistency of its Assignment publication: pods and clients may briefly hold different views of ownership during transitions. The system is designed so such transient disagreement doesn't corrupt state — but it explicitly does not provide the exclusive-ownership guarantee that leases / consensus would. Applications that need that guarantee layer it on top (or use a different system).
Seen in¶
- sources/2026-01-13-databricks-open-sourcing-dicer-auto-sharder — split-brain named as one of the three structural failure modes of static sharding that motivated Dicer.