Eliminate TString creation in Serialize

![](https://arcanum.s3.mds.yandex.net/files/azevaykin/EzeZvnh6Lzkmdlh2CvNBF)
Внутри функции TBatch::Serialize лишнее создание строки

4 files changed, 20 insertions, 15 deletions

diff --git a/ydb/core/persqueue/blob.cpp b/ydb/core/persqueue/blob.cpp
index b35d4554490..859eafa43bc 100644
--- a/ydb/core/persqueue/blob.cpp
+++ b/ydb/core/persqueue/blob.cpp
@@ -72,7 +72,7 @@ void CheckBlob(const TKey& key, const TString& blob)
 }
 
 
-void TClientBlob::Serialize(TBuffer& res) const
+void TClientBlob::SerializeTo(TBuffer& res) const
 {
     ui32 totalSize = GetBlobSize();
     ui32 psize = res.Size();
@@ -185,13 +185,16 @@ TClientBlob TClientBlob::Deserialize(const char* data, ui32 size)
     return TClientBlob(sourceId, seqNo, dt, std::move(partData), writeTimestamp, createTimestamp, us, partitionKey, explicitHashKey);
 }
 
-TString TBatch::Serialize() {
+void TBatch::SerializeTo(TString& res) {
     Y_VERIFY(Packed);
-    TString res;
+
     ui16 sz = Header.ByteSize();
-    bool rs = Header.SerializeToString(&res);
+    res.append((const char*)&sz, sizeof(ui16));
+
+    bool rs = Header.AppendToString(&res);
     Y_VERIFY(rs);
-    return TStringBuf((const char*)&sz, sizeof(ui16)) + res + PackedData;
+
+    res += PackedData;
 }
 
 template <typename TCodec>
@@ -371,7 +374,7 @@ void TBatch::Pack() {
         Header.SetFormat(NKikimrPQ::TBatchHeader::EUncompressed);
         res.Clear();
         for (ui32 i = 0; i < Blobs.size(); ++i) {
-            Blobs[i].Serialize(res);
+            Blobs[i].SerializeTo(res);
         }
         PackedData = TString{res.Data(), res.Size()};
         Header.SetPayloadSize(PackedData.size());
@@ -760,7 +763,7 @@ TString TPartitionedBlob::CompactHead(bool glueHead, THead& head, bool glueNewHe
     if (glueHead) {
         for (ui32 pp = 0; pp < head.Batches.size(); ++pp) {
             Y_VERIFY(head.Batches[pp].Packed);
-            valueD += head.Batches[pp].Serialize();
+            head.Batches[pp].SerializeTo(valueD);
         }
     }
     if (glueNewHead) {
@@ -774,7 +777,7 @@ TString TPartitionedBlob::CompactHead(bool glueHead, THead& head, bool glueNewHe
                 b = &batch;
             }
             Y_VERIFY(b->Packed);
-            valueD += b->Serialize();
+            b->SerializeTo(valueD);
         }
     }
     return valueD;
@@ -815,7 +818,7 @@ std::pair<TKey, TString> TPartitionedBlob::Add(TClientBlob&& blob)
             Blobs.clear();
             batch.Pack();
             Y_VERIFY(batch.Packed);
-            valueD += batch.Serialize();
+            batch.SerializeTo(valueD);
         }
         res.second = valueD;
         Y_VERIFY(res.second.size() <= MaxBlobSize && (res.second.size() + size + 1_MB > MaxBlobSize
diff --git a/ydb/core/persqueue/blob.h b/ydb/core/persqueue/blob.h
index 244349edfed..5f9ef43914f 100644
--- a/ydb/core/persqueue/blob.h
+++ b/ydb/core/persqueue/blob.h
@@ -92,7 +92,7 @@ struct TClientBlob {
 
     static const ui32 OVERHEAD = sizeof(ui32)/*totalSize*/ + sizeof(ui64)/*SeqNo*/ + sizeof(ui16) /*SourceId*/ + sizeof(ui64) /*WriteTimestamp*/ + sizeof(ui64) /*CreateTimestamp*/;
 
-    void Serialize(TBuffer& buffer) const;
+    void SerializeTo(TBuffer& buffer) const;
     static TClientBlob Deserialize(const char *data, ui32 size);
 
 };
@@ -189,7 +189,7 @@ struct TBatch {
     void UnpackToType0(TVector<TClientBlob> *result);
     void UnpackToType1(TVector<TClientBlob> *result);
 
-    TString Serialize();
+    void SerializeTo(TString& res);
 
     ui32 FindPos(const ui64 offset, const ui16 partNo) const;
 
diff --git a/ydb/core/persqueue/partition_write.cpp b/ydb/core/persqueue/partition_write.cpp
index 12ed674b7da..c9910b8d4f9 100644
--- a/ydb/core/persqueue/partition_write.cpp
+++ b/ydb/core/persqueue/partition_write.cpp
@@ -1147,12 +1147,12 @@ void TPartition::AddNewWriteBlob(std::pair<TKey, ui32>& res, TEvKeyValue::TEvReq
         Y_VERIFY(Head.Batches[pp].GetPartNo() == key.GetPartNo());
         for (; pp < Head.Batches.size(); ++pp) { //TODO - merge small batches here
             Y_VERIFY(Head.Batches[pp].Packed);
-            valueD += Head.Batches[pp].Serialize();
+            Head.Batches[pp].SerializeTo(valueD);
         }
     }
     for (auto& b : NewHead.Batches) {
         Y_VERIFY(b.Packed);
-        valueD += b.Serialize();
+        b.SerializeTo(valueD);
     }
 
     Y_VERIFY(res.second >= valueD.size());
diff --git a/ydb/core/persqueue/ut/internals_ut.cpp b/ydb/core/persqueue/ut/internals_ut.cpp
index ce426c4ea38..22db0517609 100644
--- a/ydb/core/persqueue/ut/internals_ut.cpp
+++ b/ydb/core/persqueue/ut/internals_ut.cpp
@@ -52,7 +52,8 @@ void Test(bool headCompacted, ui32 parts, ui32 partSize, ui32 leftInHead)
     UNIT_ASSERT(head.Batches.back().Header.GetFormat() == NKikimrPQ::TBatchHeader::ECompressed);
     head.Batches.back().Unpack();
     head.Batches.back().Pack();
-    TString str = head.Batches.back().Serialize();
+    TString str;
+    head.Batches.back().SerializeTo(str);
     auto header = ExtractHeader(str.c_str(), str.size());
     TBatch batch(header, str.c_str() + header.ByteSize() + sizeof(ui16));
     batch.Unpack();
@@ -186,7 +187,8 @@ Y_UNIT_TEST(TestBatchPacking) {
     batch.Unpack();
     batch.Pack();
     UNIT_ASSERT(batch.PackedData == s);
-    TString str = batch.Serialize();
+    TString str;
+    batch.SerializeTo(str);
     auto header = ExtractHeader(str.c_str(), str.size());
     TBatch batch2(header, str.c_str() + header.ByteSize() + sizeof(ui16));
     batch2.Unpack();