kvserver: (also) pause snapshots to paused followers

Release note: None

pkg/kv/kvserver/raft_snapshot_queue.go

@@ -139,6 +139,18 @@ func (rq *raftSnapshotQueue) processRaftSnapshot(
 			return false, nil
 		}
 	}
+	repl.mu.RLock()
+	_, destPaused := repl.mu.pausedFollowers[id]
+	repl.mu.RUnlock()
+	if ioThresh := repl.store.ioOverloadedStores.Load()[repDesc.StoreID]; ioThresh != nil && destPaused {
+		// If the destination is paused, be more hesitant to send snapshots. The destination being
+		// paused implies that we have recently checked that it's not required for quorum, and that
+		// we wish to conserve I/O on that store, which sending a snapshot counteracts. So hold back on
+		// the snapshot as well.
+		err := errors.Errorf("skipping snapshot; %s is overloaded: %s", repDesc, ioThresh)
+		repl.reportSnapshotStatus(ctx, repDesc.ReplicaID, err)
+		return false, err
+	}
 
 	err := repl.sendSnapshot(ctx, repDesc, snapType, kvserverpb.SnapshotRequest_RECOVERY)