implement chain index to make lookbacks faster

chain/store/index.go

@@ -0,0 +1,144 @@
+package store
+
+import (
+	"context"
+
+	"github.com/filecoin-project/lotus/chain/types"
+	"github.com/filecoin-project/specs-actors/actors/abi"
+	lru "github.com/hashicorp/golang-lru"
+	"golang.org/x/xerrors"
+)
+
+type ChainIndex struct {
+	skipCache *lru.ARCCache
+
+	loadTipSet loadTipSetFunc
+
+	skipLength abi.ChainEpoch
+}
+type loadTipSetFunc func(types.TipSetKey) (*types.TipSet, error)
+
+func NewChainIndex(lts loadTipSetFunc) *ChainIndex {
+	sc, _ := lru.NewARC(8192)
+	return &ChainIndex{
+		skipCache:  sc,
+		loadTipSet: lts,
+		skipLength: 20,
+	}
+}
+
+type lbEntry struct {
+	ts           *types.TipSet
+	parentHeight abi.ChainEpoch
+	target       types.TipSetKey
+}
+
+func (ci *ChainIndex) GetTipsetByHeight(ctx context.Context, from *types.TipSet, to abi.ChainEpoch) (*types.TipSet, error) {
+	if from.Height()-to <= ci.skipLength {
+		return ci.walkBack(from, to)
+	}
+
+	rounded, err := ci.roundDown(from)
+	if err != nil {
+		return nil, err
+	}
+
+	cur := rounded.Key()
+	for {
+		cval, ok := ci.skipCache.Get(cur)
+		if !ok {
+			fc, err := ci.fillCache(cur)
+			if err != nil {
+				return nil, err
+			}
+			cval = fc
+		}
+
+		lbe := cval.(*lbEntry)
+		if lbe.ts.Height() == to || lbe.parentHeight < to {
+			return lbe.ts, nil
+		} else if to > lbe.ts.Height()-ci.skipLength {
+			return ci.walkBack(from, to)
+		}
+
+		cur = lbe.target
+	}
+}
+
+func (ci *ChainIndex) fillCache(tsk types.TipSetKey) (*lbEntry, error) {
+	ts, err := ci.loadTipSet(tsk)
+	if err != nil {
+		return nil, err
+	}
+
+	// will either be equal to ts.Height, or at least > ts.Parent.Height()
+	rheight := ci.roundHeight(ts.Height())
+
+	parent, err := ci.loadTipSet(ts.Parents())
+	if err != nil {
+		return nil, err
+	}
+
+	if parent.Height() > rheight {
+		return nil, xerrors.Errorf("cache is inconsistent")
+	}
+
+	rheight -= ci.skipLength
+
+	skipTarget, err := ci.walkBack(parent, rheight)
+	if err != nil {
+		return nil, err
+	}
+
+	lbe := &lbEntry{
+		ts:           ts,
+		parentHeight: parent.Height(),
+		target:       skipTarget.Key(),
+	}
+	ci.skipCache.Add(tsk, lbe)
+
+	return lbe, nil
+}
+
+func (ci *ChainIndex) roundHeight(h abi.ChainEpoch) abi.ChainEpoch {
+	return abi.ChainEpoch(h/ci.skipLength) * ci.skipLength
+}
+
+func (ci *ChainIndex) roundDown(ts *types.TipSet) (*types.TipSet, error) {
+	target := ci.roundHeight(ts.Height())
+
+	rounded, err := ci.walkBack(ts, target)
+	if err != nil {
+		return nil, err
+	}
+
+	return rounded, nil
+}
+
+func (ci *ChainIndex) walkBack(from *types.TipSet, to abi.ChainEpoch) (*types.TipSet, error) {
+	if to > from.Height() {
+		return nil, xerrors.Errorf("looking for tipset with height greater than start point")
+	}
+
+	if to == from.Height() {
+		return from, nil
+	}
+
+	ts := from
+
+	for {
+		pts, err := ci.loadTipSet(ts.Parents())
+		if err != nil {
+			return nil, err
+		}
+
+		if to > pts.Height() {
+			return ts, nil
+		}
+		if to == pts.Height() {
+			return pts, nil
+		}
+
+		ts = pts
+	}
+}

chain/store/store.go

@@ -62,6 +62,8 @@ type ChainStore struct {
 	tstLk   sync.Mutex
 	tipsets map[abi.ChainEpoch][]cid.Cid
 
+	cindex *ChainIndex
+
 	reorgCh          chan<- reorg
 	headChangeNotifs []func(rev, app []*types.TipSet) error
 
@@ -84,6 +86,10 @@ func NewChainStore(bs bstore.Blockstore, ds dstore.Batching, vmcalls runtime.Sys
 		vmcalls:  vmcalls,
 	}
 
+	ci := NewChainIndex(cs.LoadTipSet)
+
+	cs.cindex = ci
+
 	cs.reorgCh = cs.reorgWorker(context.TODO())
 
 	hcnf := func(rev, app []*types.TipSet) error {
@@ -951,24 +957,16 @@ func (cs *ChainStore) GetTipsetByHeight(ctx context.Context, h abi.ChainEpoch, t
 		log.Warnf("expensive call to GetTipsetByHeight, seeking %d levels", ts.Height()-h)
 	}
 
-	for {
-		pts, err := cs.LoadTipSet(ts.Parents())
-		if err != nil {
-			return nil, err
-		}
-
-		if h > pts.Height() {
-			if prev {
-				return pts, nil
-			}
-			return ts, nil
-		}
-		if h == pts.Height() {
-			return pts, nil
-		}
-
-		ts = pts
+	lbts, err := cs.cindex.GetTipsetByHeight(ctx, ts, h)
+	if err != nil {
+		return nil, err
 	}
+
+	if lbts.Height() == h || !prev {
+		return lbts, nil
+	}
+
+	return cs.LoadTipSet(lbts.Parents())
 }
 
 func recurseLinks(bs blockstore.Blockstore, root cid.Cid, in []cid.Cid) ([]cid.Cid, error) {