Add FullNeeded() to Snapshot store

It may be necessary to override the FullNeeded definition, so wrap it.

snapshot/sink_test.go

@@ -107,6 +107,12 @@ func Test_SinkFullSnapshot(t *testing.T) {
 		t.Fatalf("Snapshot data does not match")
 	}
 
+	if fn, err := store.FullNeeded(); err != nil {
+		t.Fatalf("Failed to check if full snapshot needed: %v", err)
+	} else if fn {
+		t.Errorf("Expected full snapshot not to be needed, but it is")
+	}
+
 	// Write a second full snapshot, it should be installed without issue.
 	sink = NewSink(store, makeRaftMeta("snap-5678", 4, 3, 2))
 	if sink == nil {
@@ -206,6 +212,17 @@ func Test_SinkCreateFullThenWALSnapshots(t *testing.T) {
 		if err := sink.Close(); err != nil {
 			t.Fatalf("Failed to close sink: %v", err)
 		}
+
+		if fn, err := store.FullNeeded(); err != nil {
+			t.Fatalf("Failed to check if full snapshot needed: %v", err)
+		} else if fn {
+			t.Errorf("Expected full snapshot not to be needed, but it is")
+		}
+	}
+	if fn, err := store.FullNeeded(); err != nil {
+		t.Fatalf("Failed to check if full snapshot needed: %v", err)
+	} else if !fn {
+		t.Errorf("Expected full snapshot to be needed, but it is not")
 	}
 	createSnapshot("snap-1234", 3, 2, 1, "testdata/db-and-wals/backup.db")
 	createSnapshot("snap-2345", 4, 3, 2, "testdata/db-and-wals/wal-00")

snapshot/store.go

@@ -151,6 +151,15 @@ func (s *Store) Open(id string) (*raft.SnapshotMeta, io.ReadCloser, error) {
 	return meta, fd, nil
 }
 
+// FullNeeded returns true if a full snapshot is needed.
+func (s *Store) FullNeeded() (bool, error) {
+	snaps, err := s.getSnapshots()
+	if err != nil {
+		return false, err
+	}
+	return len(snaps) == 0, nil
+}
+
 // Stats returns stats about the Snapshot Store.
 func (s *Store) Stats() (map[string]interface{}, error) {
 	snapshots, err := s.getSnapshots()

snapshot/store_test.go

@@ -94,6 +94,12 @@ func Test_StoreEmpty(t *testing.T) {
 		t.Errorf("Expected no snapshots, got %d", len(snaps))
 	}
 
+	if fn, err := store.FullNeeded(); err != nil {
+		t.Fatalf("Failed to check if full snapshot needed: %v", err)
+	} else if !fn {
+		t.Errorf("Expected full snapshot needed, but it is not")
+	}
+
 	_, _, err = store.Open("non-existent")
 	if err == nil {
 		t.Fatalf("Expected error opening non-existent snapshot, got nil")

store/store.go

@@ -159,6 +159,9 @@ func ResetStats() {
 type SnapshotStore interface {
 	raft.SnapshotStore
 
+	// FullNeeded returns true if a full snapshot is needed.
+	FullNeeded() (bool, error)
+
 	// Stats returns stats about the Snapshot Store.
 	Stats() (map[string]interface{}, error)
 }
@@ -1668,12 +1671,10 @@ func (s *Store) Database(leader bool) ([]byte, error) {
 func (s *Store) Snapshot() (raft.FSMSnapshot, error) {
 	startT := time.Now()
 
-	currSnaps, err := s.snapshotStore.List()
+	fullNeeded, err := s.snapshotStore.FullNeeded()
 	if err != nil {
 		return nil, err
 	}
-	fullNeeded := len(currSnaps) == 0
-
 	fPLog := fullPretty(fullNeeded)
 	s.logger.Printf("initiating %s snapshot on node ID %s", fPLog, s.raftID)
 	defer func() {