Module migration_executor 

vShard migration executor — drives the 3-phase migration state machine.

Phase 1 (Base Copy): Add target node to source Raft group as learner. Raft replication handles data transfer (AppendEntries with committed log entries).

Phase 2 (WAL Catch-Up): Monitor target’s replication lag. When the target’s commit_index is within threshold of the leader’s, catch-up is ready.

Phase 3 (Atomic Cut-Over): Propose a routing table update through Raft. Once committed on all replicas, the vShard is atomically owned by the target group. Create ghost stubs on the source for transparent scatter-gather.

Structs

MigrationExecutor

Executes a vShard migration through the 3-phase protocol.

MigrationRequest

Configuration for a vShard migration.

MigrationResult

Result of a completed migration.

MigrationSnapshot

Observability snapshot of a migration.

MigrationTracker

Track active migrations across the cluster.