| name | 0.4.6-understand-split_brain |
| description | [0.4.6] Scenario where network partition causes multiple nodes to believe they are leader; resolved by quorum. |
understand-split_brain
CALL NUMBER: distributed_consensus_and_replication_protocols.split_brain : deep_consensus(7), deep_raft(6)
DEFINITION: Scenario where network partition causes multiple nodes to believe they are leader; resolved by quorum.
Invoke this skill to understand split_brain down to its primitives. The RELATIVE ROOT below is the least-fixed-point closure of everything it bundles from — the full import cone, grouped by the lib each prim comes from. Projected from a prover-typed KB (MAP/SWI-Prolog consistency gate): every reference below resolves.
THE RELATIVE ROOT (the import cone, by lib)
from ?
- agreement (d4): The property that a set of distributed processes reach the same decision outcome on a given value. Uniform agreement requires all processes including those that later crash to decide identically; asymmetric agreement permits different decision classes for different process roles such as primary versus backup.
from deep_consensus
- availability (d1): Probability system remains operational and accessible despite failures.
- safety (d1): Property requiring system never reaches inconsistent or invalid state.
- liveness (d2): Property requiring system to eventually respond or make progress under fair conditions.
- quorum_read (d2): Reading from sufficient replicas to guarantee seeing latest write.
- quorum_write (d2): Writing to sufficient replicas to guarantee subsequent readers see the value.
- replication_factor (d2): Count of replica copies maintained for durability and availability.
- strong_quorum (d2): Quorum where read and write quorums overlap (r + w > n).
from deep_raft
- a007 (d4): Quorum in agreement: a subset of processes sufficient to guarantee agreement can be reached, typically intersecting any valid quorum to ensure overlap.
- a008 (d4): Threshold in agreement: the minimum number of correct processes required to guarantee safety and liveness under given failure assumptions.
- a009 (d5): Asymmetric agreement: one class of processes (e.g., primary) must agree while another class (e.g., backups) may reach different decisions, used in primary-backup protocols.
- a002 (d5): Validity in agreement: the decided value must have been proposed by some process in the system, guaranteeing agreements are grounded in actual proposals.
- a005 (d6): Uniform agreement: all processes including those that later fail must decide on the same value, stricter than ordinary agreement which only binds correct processes.
- a004 (d6): Termination in agreement: every correct process eventually decides some value, ensuring the protocol makes progress and does not stall indefinitely.
from distributed_consensus_and_replication_protocols
- quorum (d1): Subset of nodes sufficient for reads or writes; typically majority (n/2+1) for strong consistency.
- linearizability (d2): Strongest consistency model: every operation appears atomic and ordered in real time across all nodes.
- semi_synchronous_replication (d2): Write waits for quorum of replicas to acknowledge; balances latency and durability.
- synchronous_replication (d2): Write waits for all replicas to acknowledge before returning to client.
- consensus (d3): Agreement on a single value among a set of distributed processes; the core problem consensus protocols solve.
- fault_tolerance (d4): System's ability to continue operating correctly despite component failures.
- replicated_log (d5): Ordered log of commands maintained across replicas; foundation of state machine replication.
CONSUMERS (what needs this)
fencing_token, network_partition
Projected from the distributed consensus and replication protocols KB (196 concepts / 187 relations) — consistency-typed by MAP; the facet list after the colon IS the cross-lib dependency web.
(leaf — this is an actual skill.)
