use a missing compactionIndex as an indicator for warmup

so that splitstore v0 nodes upgrading will get a fresh warmup.

blockstore/splitstore/splitstore.go

@@ -485,6 +485,9 @@ func (s *SplitStore) Start(chain ChainAccessor) error {
 	s.chain = chain
 	curTs := chain.GetHeaviestTipSet()
 
+	// should we warmup
+	warmup := false
+
 	// load base epoch from metadata ds
 	// if none, then use current epoch because it's a fresh start
 	bs, err := s.ds.Get(baseEpochKey)
@@ -514,11 +517,7 @@ func (s *SplitStore) Start(chain ChainAccessor) error {
 		s.warmupEpoch = bytesToEpoch(bs)
 
 	case dstore.ErrNotFound:
-		// the hotstore hasn't warmed up, start a concurrent warm up
+		warmup = true
-		err = s.warmup(curTs)
-		if err != nil {
-			return xerrors.Errorf("error warming up: %w", err)
-		}
 
 	default:
 		return xerrors.Errorf("error loading warmup epoch: %w", err)
@@ -542,12 +541,22 @@ func (s *SplitStore) Start(chain ChainAccessor) error {
 		s.compactionIndex = bytesToInt64(bs)
 
 	case dstore.ErrNotFound:
+		// this is potentially an upgrade from splitstore v0; schedule a warmup as v0 has
+		// some issues with hot references leaking into the coldstore.
+		warmup = true
 	default:
 		return xerrors.Errorf("error loading compaction index: %w", err)
 	}
 
 	log.Infow("starting splitstore", "baseEpoch", s.baseEpoch, "warmupEpoch", s.warmupEpoch)
 
+	if warmup {
+		err = s.warmup(curTs)
+		if err != nil {
+			return xerrors.Errorf("error starting warmup: %w", err)
+		}
+	}
+
 	// watch the chain
 	chain.SubscribeHeadChanges(s.HeadChange)
 
@@ -959,6 +968,12 @@ func (s *SplitStore) doWarmup(curTs *types.TipSet) error {
 	s.warmupEpoch = epoch
 	s.mx.Unlock()
 
+	// also save the compactionIndex, as this is used as an indicator of warmup for upgraded nodes
+	err = s.ds.Put(compactionIndexKey, int64ToBytes(s.compactionIndex))
+	if err != nil {
+		return xerrors.Errorf("error saving compaction index: %w", err)
+	}
+
 	return nil
 }