native: optimize NEO's committee/validators cache handling

Do not recalculate new committee/validators value in the start of every
subsequent epoch. Use values that was calculated in the PostPersist method
of the previously processed block in the end of the previous epoch.

Signed-off-by: Anna Shaleva <shaleva.ann@nspcc.ru>

pkg/core/native/native_neo.go

@@ -63,8 +63,13 @@ type NeoCache struct {
 	// (every 28 blocks for mainnet). It's value
 	// is always equal to the value stored by `prefixCommittee`.
 	committee keysWithVotes
+	// newEpochCommittee contains cached committee members updated once per dBFT
+	// epoch in PostPersist of the last block in the epoch.
+	newEpochCommittee keysWithVotes
 	// committeeHash contains the script hash of the committee.
 	committeeHash util.Uint160
+	// newEpochCommitteeHash contains the script hash of the newEpochCommittee.
+	newEpochCommitteeHash util.Uint160
 
 	// gasPerVoteCache contains the last updated value of GAS per vote reward for candidates.
 	// It is set in state-modifying methods only and read in `PostPersist`, thus is not protected
@@ -276,7 +281,11 @@ func (n *NEO) Initialize(ic *interop.Context) error {
 	cache := &NeoCache{
 		gasPerVoteCache: make(map[string]big.Int),
 		votesChanged:    true,
-		newEpochNextValidators: nil, // will be updated in the last epoch block's PostPersist right before the committee update block.
+		// Will be updated in the last epoch block's PostPersist right before the committee update block.
+		// NeoToken's deployment (and initialization) isn't intended to be performed not-in-genesis block anyway.
+		newEpochNextValidators: nil,
+		newEpochCommittee:      nil,
+		newEpochCommitteeHash:  util.Uint160{},
 	}
 
 	// We need cache to be present in DAO before the subsequent call to `mint`.
@@ -319,11 +328,13 @@ func (n *NEO) InitializeCache(blockHeight uint32, d *dao.Simple) error {
 	cache := &NeoCache{
 		gasPerVoteCache: make(map[string]big.Int),
 		votesChanged:    true,
-		// If it's a block in the middle of dbft epoch, then no one must access
+		// If it's a block in the middle of dBFT epoch, then no one must access
-		// this field, and it will be updated during the PostPersist of the last
+		// these NewEpoch* fields, and they will be updated during the PostPersist of the last
-		// block in the current epoch. If it's the laast block of the current epoch,
+		// block in the current epoch. If it's the last block of the current epoch,
 		// then update this cache manually below.
 		newEpochNextValidators: nil,
+		newEpochCommittee:      nil,
+		newEpochCommitteeHash:  util.Uint160{},
 	}
 
 	var committee = keysWithVotes{}
@@ -338,13 +349,13 @@ func (n *NEO) InitializeCache(blockHeight uint32, d *dao.Simple) error {
 	cache.gasPerBlock = n.getSortedGASRecordFromDAO(d)
 	cache.registerPrice = getIntWithKey(n.ID, d, []byte{prefixRegisterPrice})
 
-	// Update next block validators cache for external users if committee should be
+	// Update newEpoch* cache for external users if committee should be
 	// updated in the next block.
 	if n.cfg.ShouldUpdateCommitteeAt(blockHeight + 1) {
 		var numOfCNs = n.cfg.GetNumOfCNs(blockHeight + 1)
-		err := n.updateCachedValidators(d, cache, blockHeight, numOfCNs)
+		err := n.updateCachedNewEpochValues(d, cache, blockHeight, numOfCNs)
 		if err != nil {
-			return fmt.Errorf("failed to update next block newEpochNextValidators cache: %w", err)
+			return fmt.Errorf("failed to update next block newEpoch* cache: %w", err)
 		}
 	}
 
@@ -376,37 +387,28 @@ func (n *NEO) updateCache(cache *NeoCache, cvs keysWithVotes, blockHeight uint32
 	return nil
 }
 
-// updateCachedValidators sets newEpochNextValidators cache that will be used by external users
+// updateCachedNewEpochValues sets newEpochNextValidators, newEpochCommittee and
-// to retrieve next block validators list of the next dBFT epoch that wasn't yet
+// newEpochCommitteeHash cache that will be used by external users to retrieve
-// started. Thus, it stores the list of validators computed using the persisted
+// next block validators list of the next dBFT epoch that wasn't yet started and
-// blocks state of the latest epoch.
+// will be used by corresponding values initialisation on the next epoch start.
-func (n *NEO) updateCachedValidators(d *dao.Simple, cache *NeoCache, blockHeight uint32, numOfCNs int) error {
+// The updated new epoch cached values computed using the persisted blocks state
-	result, _, err := n.computeCommitteeMembers(blockHeight, d)
+// of the latest epoch.
+func (n *NEO) updateCachedNewEpochValues(d *dao.Simple, cache *NeoCache, blockHeight uint32, numOfCNs int) error {
+	committee, cvs, err := n.computeCommitteeMembers(blockHeight, d)
 	if err != nil {
 		return fmt.Errorf("failed to compute committee members: %w", err)
 	}
-	result = result[:numOfCNs]
+	cache.newEpochCommittee = cvs
-	sort.Sort(result)
-	cache.newEpochNextValidators = result
-	return nil
-}
 
-func (n *NEO) updateCommittee(cache *NeoCache, ic *interop.Context) error {
+	script, err := smartcontract.CreateMajorityMultiSigRedeemScript(committee.Copy())
-	if !cache.votesChanged {
-		// We need to put in storage anyway, as it affects dumps
-		ic.DAO.PutStorageItem(n.ID, prefixCommittee, cache.committee.Bytes(ic.DAO.GetItemCtx()))
-		return nil
-	}
-
-	_, cvs, err := n.computeCommitteeMembers(ic.BlockHeight(), ic.DAO)
 	if err != nil {
 		return err
 	}
-	if err := n.updateCache(cache, cvs, ic.BlockHeight()); err != nil {
+	cache.newEpochCommitteeHash = hash.Hash160(script)
-		return err
+
-	}
+	nextVals := committee[:numOfCNs].Copy()
-	cache.votesChanged = false
+	sort.Sort(nextVals)
-	ic.DAO.PutStorageItem(n.ID, prefixCommittee, cvs.Bytes(ic.DAO.GetItemCtx()))
+	cache.newEpochNextValidators = nextVals
 	return nil
 }
 
@@ -414,15 +416,20 @@ func (n *NEO) updateCommittee(cache *NeoCache, ic *interop.Context) error {
 func (n *NEO) OnPersist(ic *interop.Context) error {
 	if n.cfg.ShouldUpdateCommitteeAt(ic.Block.Index) {
 		cache := ic.DAO.GetRWCache(n.ID).(*NeoCache)
+		// Cached newEpoch* values always have proper value set (either by PostPersist
+		// during the last epoch block handling or by initialization code).
 		oldKeys := cache.nextValidators
 		oldCom := cache.committee
 		if n.cfg.GetNumOfCNs(ic.Block.Index) != len(oldKeys) ||
 			n.cfg.GetCommitteeSize(ic.Block.Index) != len(oldCom) {
-			cache.votesChanged = true
+			cache.nextValidators = cache.newEpochNextValidators
-		}
+			cache.committee = cache.newEpochCommittee
-		if err := n.updateCommittee(cache, ic); err != nil {
+			cache.committeeHash = cache.newEpochCommitteeHash
-			return err
+			cache.votesChanged = false
 		}
+
+		// We need to put in storage anyway, as it affects dumps
+		ic.DAO.PutStorageItem(n.ID, prefixCommittee, cache.committee.Bytes(ic.DAO.GetItemCtx()))
 	}
 	return nil
 }
@@ -475,8 +482,9 @@ func (n *NEO) PostPersist(ic *interop.Context) error {
 			}
 		}
 	}
-	// Update next block newEpochNextValidators cache for external users if committee should be
+	// Update newEpoch cache for external users and further committee, committeeHash
-	// updated in the next block.
+	// and nextBlockValidators cache initialisation if committee should be updated in
+	// the next block.
 	if n.cfg.ShouldUpdateCommitteeAt(ic.Block.Index + 1) {
 		var (
 			h        = ic.Block.Index // consider persisting block as stored to get _next_ block newEpochNextValidators
@@ -486,9 +494,9 @@ func (n *NEO) PostPersist(ic *interop.Context) error {
 			if !isCacheRW {
 				cache = ic.DAO.GetRWCache(n.ID).(*NeoCache)
 			}
-			err := n.updateCachedValidators(ic.DAO, cache, h, numOfCNs)
+			err := n.updateCachedNewEpochValues(ic.DAO, cache, h, numOfCNs)
 			if err != nil {
-				return fmt.Errorf("failed to update next block newEpochNextValidators cache: %w", err)
+				return fmt.Errorf("failed to update next block newEpoch* cache: %w", err)
 			}
 		}
 	}