From 0917fc3de7285e1b6a0a5d39699b9ad32a9dd3b2 Mon Sep 17 00:00:00 2001
From: Jae Kwon <jae@tendermint.com>
Date: Sun, 3 Dec 2017 23:17:10 -0800
Subject: [PATCH] rootMultiStore holds lastCommitID

---
 store/cachemultistore.go |  2 +-
 store/rootmultistore.go  | 28 +++++++---------------------
 2 files changed, 8 insertions(+), 22 deletions(-)

diff --git a/store/cachemultistore.go b/store/cachemultistore.go
index 001e05c4ce..9f9be0830b 100644
--- a/store/cachemultistore.go
+++ b/store/cachemultistore.go
@@ -16,7 +16,7 @@ type cacheMultiStore struct {
 
 func newCacheMultiStore(rs *rootMultiStore) cacheMultiStore {
 	cms := cacheMultiStore{
-		db:           dbm.CacheDB(),
+		db:           rs.db.CacheDB(),
 		version:      rs.curVersion,
 		lastCommitID: rs.lastCommitID,
 		substores:    make(map[string]CacheWriter, len(rs.substores)),
diff --git a/store/rootmultistore.go b/store/rootmultistore.go
index e6b7409dd0..d45f96fc04 100644
--- a/store/rootmultistore.go
+++ b/store/rootmultistore.go
@@ -21,7 +21,7 @@ const (
 type rootMultiStore struct {
 	db           dbm.DB
 	curVersion   int64
-	lastHash     []byte
+	lastCommitID CommitID
 	storeLoaders map[string]CommitStoreLoader
 	substores    map[string]CommitStore
 }
@@ -30,7 +30,6 @@ func NewMultiStore(db dbm.DB) *rootMultiStore {
 	return &rootMultiStore{
 		db:           db,
 		curVersion:   0,
-		lastHash:     nil,
 		storeLoaders: make(map[string]CommitStoreLoader),
 		substores:    make(map[string]CommitStore),
 	}
@@ -64,7 +63,7 @@ func (rs *rootMultiStore) LoadVersion(ver int64) error {
 				return fmt.Errorf("Failed to load rootMultiStore: %v", err)
 			}
 			rs.curVersion = 1
-			rs.lastHash = nil
+			rs.lastCommitID = CommitID{}
 			rs.substores[name] = store
 		}
 		return nil
@@ -98,7 +97,7 @@ func (rs *rootMultiStore) LoadVersion(ver int64) error {
 
 	// Success.
 	rs.curVersion = ver + 1
-	rs.lastHash = state.LastHash
+	rs.lastCommitID = state.CommitID()
 	rs.substores = newSubstores
 	return nil
 }
@@ -106,7 +105,6 @@ func (rs *rootMultiStore) LoadVersion(ver int64) error {
 // Commits each substore and gets commitState.
 func (rs *rootMultiStore) doCommit() commitState {
 	version := rs.curVersion
-	lastHash := rs.LastHash
 	substores := make([]substore, len(rs.substores))
 
 	for name, store := range rs.substores {
@@ -127,7 +125,6 @@ func (rs *rootMultiStore) doCommit() commitState {
 
 	return commitState{
 		Version:   version,
-		LastHash:  lastHash,
 		Substores: substores,
 	}
 }
@@ -157,11 +154,12 @@ func (rs *rootMultiStore) Commit() CommitID {
 
 	batch.Write()
 	rs.version += 1
-
-	return CommitID{
+	commitID := CommitID{
 		Version: version,
 		Hash:    state.Hash(),
 	}
+	rs.lastCommitID = commitID
+	return commitID
 }
 
 // Implements CommitStore
@@ -171,16 +169,7 @@ func (rs *rootMultiStore) CacheWrap() CacheWriter {
 
 // Get the last committed CommitID
 func (rs *rootMultiStore) LastCommitID() CommitID {
-
-	// If we haven't committed yet, return a zero CommitID
-	if rs.curVersion == 0 {
-		return CommitID{}
-	}
-
-	return CommitID{
-		Version: rs.curVersion - 1,
-		Hash:    rs.LastHash,
-	}
+	return rs.lastCommitID
 }
 
 // Implements MultiStore
@@ -212,9 +201,6 @@ type commitState struct {
 	// Version
 	Version int64
 
-	// Last hash (memoization)
-	LastHash []byte
-
 	// Substore info for
 	Substores []substore
 }