storage: Added checks for invariants

storage/local/persistence.go

@@ -706,6 +706,9 @@ func (p *persistence) checkpointSeriesMapAndHeads(fingerprintToSeries *seriesMap
 				}
 			}
 			// chunkDescsOffset.
+			if m.series.chunkDescsOffset < 0 && m.series.persistWatermark > 0 {
+				panic("encountered unknown chunk desc offset in combination with positive persist watermark")
+			}
 			if _, err = codable.EncodeVarint(w, int64(m.series.chunkDescsOffset+m.series.persistWatermark)); err != nil {
 				return
 			}

storage/local/series.go

@@ -283,6 +283,9 @@ func (s *memorySeries) evictChunkDescs(lenToEvict int) {
 	if lenToEvict < 1 {
 		return
 	}
+	if s.chunkDescsOffset < 0 {
+		panic("chunk desc eviction requested with unknown chunk desc offset")
+	}
 	lenToKeep := len(s.chunkDescs) - lenToEvict
 	s.savedFirstTime = s.firstTime()
 	s.chunkDescsOffset += lenToEvict