From b22495767727e25d2abe812ee13b855fe0f5cb96 Mon Sep 17 00:00:00 2001
From: Roman Khimov <roman@nspcc.ru>
Date: Thu, 3 Feb 2022 11:46:09 +0300
Subject: [PATCH] storage: attempt to Clone

Allows to regain ~3-4% TPS, doesn't affect chain restore time much.
---
 pkg/core/blockchain_test.go         |  2 +-
 pkg/core/dao/dao.go                 | 10 ++++++++++
 pkg/core/interop/context.go         |  2 +-
 pkg/core/storage/memcached_store.go | 20 ++++++++++++++++++++
 4 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/pkg/core/blockchain_test.go b/pkg/core/blockchain_test.go
index 492c74c1d..2739d9504 100644
--- a/pkg/core/blockchain_test.go
+++ b/pkg/core/blockchain_test.go
@@ -1116,7 +1116,7 @@ func TestVerifyHashAgainstScript(t *testing.T) {
 	bc := newTestChain(t)
 
 	cs, csInvalid := getTestContractState(t, 4, 5, random.Uint160()) // sender and IDs are not important for the test
-	ic := bc.newInteropContext(trigger.Verification, bc.dao, nil, nil)
+	ic := bc.newInteropContext(trigger.Verification, bc.dao.GetWrapped(), nil, nil)
 	require.NoError(t, bc.contracts.Management.PutContractState(bc.dao, cs))
 	require.NoError(t, bc.contracts.Management.PutContractState(bc.dao, csInvalid))
 
diff --git a/pkg/core/dao/dao.go b/pkg/core/dao/dao.go
index aff495107..faf8f585d 100644
--- a/pkg/core/dao/dao.go
+++ b/pkg/core/dao/dao.go
@@ -50,6 +50,7 @@ type DAO interface {
 	GetStorageItemsWithPrefix(id int32, prefix []byte) ([]state.StorageItemWithKey, error)
 	GetTransaction(hash util.Uint256) (*transaction.Transaction, uint32, error)
 	GetVersion() (Version, error)
+	GetCloned() DAO
 	GetWrapped() DAO
 	HasTransaction(hash util.Uint256) error
 	Persist() (int, error)
@@ -102,6 +103,15 @@ func (dao *Simple) GetWrapped() DAO {
 	return d
 }
 
+// GetCloned returns new DAO instance with shared trie of MemCachedStore, use it for
+// the latest layer that either doesn't need to Persist, or Persists to another well-known
+// non-shared (!) layer.
+func (dao *Simple) GetCloned() DAO {
+	d := *dao
+	d.Store = dao.Store.Clone()
+	return &d
+}
+
 // GetAndDecode performs get operation and decoding with serializable structures.
 func (dao *Simple) GetAndDecode(entity io.Serializable, key []byte) error {
 	entityBytes, err := dao.Store.Get(key)
diff --git a/pkg/core/interop/context.go b/pkg/core/interop/context.go
index 26a0e723c..38dd64df0 100644
--- a/pkg/core/interop/context.go
+++ b/pkg/core/interop/context.go
@@ -71,7 +71,7 @@ func NewContext(trigger trigger.Type, bc Ledger, d dao.DAO,
 	getContract func(dao.DAO, util.Uint160) (*state.Contract, error), natives []Contract,
 	block *block.Block, tx *transaction.Transaction, log *zap.Logger) *Context {
 	baseExecFee := int64(DefaultBaseExecFee)
-	dao := d.GetWrapped()
+	dao := d.GetCloned()
 
 	if bc != nil && (block == nil || block.Index != 0) {
 		baseExecFee = bc.GetBaseExecFee()
diff --git a/pkg/core/storage/memcached_store.go b/pkg/core/storage/memcached_store.go
index e922fc297..ab205016f 100644
--- a/pkg/core/storage/memcached_store.go
+++ b/pkg/core/storage/memcached_store.go
@@ -14,6 +14,9 @@ import (
 type MemCachedStore struct {
 	MemoryStore
 
+	// lowerTrie stores lower level MemCachedStore trie for cloned MemCachedStore,
+	// which allows for much more efficient Persist.
+	lowerTrie *btree.BTree
 	// plock protects Persist from double entrance.
 	plock sync.Mutex
 	// Persistent Store.
@@ -55,6 +58,16 @@ func NewMemCachedStore(lower Store) *MemCachedStore {
 	}
 }
 
+// NewClonedMemCachedStore creates a cloned MemCachedStore which shares the trie
+// with another MemCachedStore (until you write into it).
+func (s *MemCachedStore) Clone() *MemCachedStore {
+	return &MemCachedStore{
+		MemoryStore: MemoryStore{mem: *s.mem.Clone()}, // Shared COW trie.
+		lowerTrie:   &s.mem,
+		ps:          s.ps, // But the same PS.
+	}
+}
+
 // Get implements the Store interface.
 func (s *MemCachedStore) Get(key []byte) ([]byte, error) {
 	s.mut.RLock()
@@ -239,6 +252,13 @@ func (s *MemCachedStore) persist(isSync bool) (int, error) {
 	defer s.plock.Unlock()
 	s.mut.Lock()
 
+	if s.lowerTrie != nil {
+		keys = s.mem.Len() - s.lowerTrie.Len()
+		*s.lowerTrie = s.mem
+		s.mut.Unlock()
+		return keys, nil
+	}
+
 	keys = s.mem.Len()
 	if keys == 0 {
 		s.mut.Unlock()