From c88720bf45da3f56a22f90f4a73f90bbb8c6dbfc Mon Sep 17 00:00:00 2001
From: Anna Shaleva <shaleva.ann@nspcc.ru>
Date: Tue, 19 Oct 2021 13:29:43 +0300
Subject: [PATCH] core: remove memstore routine from
 (*MemCachedStore).SeekAsync

It adds unnecessary overhead to computations.
---
 pkg/core/storage/memcached_store.go | 37 +++++++++++++++--------------
 1 file changed, 19 insertions(+), 18 deletions(-)

diff --git a/pkg/core/storage/memcached_store.go b/pkg/core/storage/memcached_store.go
index ef1f1e583..5f3c168f6 100644
--- a/pkg/core/storage/memcached_store.go
+++ b/pkg/core/storage/memcached_store.go
@@ -102,7 +102,7 @@ func (s *MemCachedStore) Seek(key []byte, f func(k, v []byte)) {
 // that key-value items are sorted by key in ascending way.
 func (s *MemCachedStore) SeekAsync(ctx context.Context, key []byte, cutPrefix bool) chan KeyValue {
 	// Create memory store `mem` and `del` snapshot not to hold the lock.
-	memRes := make([]KeyValueExists, 0)
+	var memRes []KeyValueExists
 	sk := string(key)
 	s.mut.RLock()
 	for k, v := range s.MemoryStore.mem {
@@ -110,7 +110,7 @@ func (s *MemCachedStore) SeekAsync(ctx context.Context, key []byte, cutPrefix bo
 			memRes = append(memRes, KeyValueExists{
 				KeyValue: KeyValue{
 					Key:   []byte(k),
-					Value: slice.Copy(v),
+					Value: v,
 				},
 				Exists: true,
 			})
@@ -133,23 +133,9 @@ func (s *MemCachedStore) SeekAsync(ctx context.Context, key []byte, cutPrefix bo
 	})
 
 	var (
-		data1   = make(chan KeyValueExists)
 		data2   = make(chan KeyValue)
 		seekres = make(chan KeyValue)
 	)
-	// Seek over memory store.
-	go func() {
-	loop:
-		for _, kv := range memRes {
-			select {
-			case <-ctx.Done():
-				break loop
-			default:
-				data1 <- kv
-			}
-		}
-		close(data1)
-	}()
 
 	// Seek over persistent store.
 	go func() {
@@ -174,7 +160,16 @@ func (s *MemCachedStore) SeekAsync(ctx context.Context, key []byte, cutPrefix bo
 
 	// Merge results of seek operations in ascending order.
 	go func() {
-		kvMem, haveMem := <-data1
+		var (
+			kvMem   KeyValueExists
+			haveMem bool
+			iMem    int
+		)
+		if iMem < len(memRes) {
+			kvMem = memRes[iMem]
+			haveMem = true
+			iMem++
+		}
 		kvPs, havePs := <-data2
 		for {
 			if !haveMem && !havePs {
@@ -191,7 +186,13 @@ func (s *MemCachedStore) SeekAsync(ctx context.Context, key []byte, cutPrefix bo
 						Value: kvMem.Value,
 					}
 				}
-				kvMem, haveMem = <-data1
+				if iMem < len(memRes) {
+					kvMem = memRes[iMem]
+					haveMem = true
+					iMem++
+				} else {
+					haveMem = false
+				}
 			} else {
 				if !bytes.Equal(kvMem.Key, kvPs.Key) {
 					if cutPrefix {