DataShard stats iterator avoid allocations

4 files changed, 53 insertions, 44 deletions

diff --git a/ydb/core/scheme/scheme_tablecell.cpp b/ydb/core/scheme/scheme_tablecell.cpp
index 04f168be3a..e25ee1ad64 100644
--- a/ydb/core/scheme/scheme_tablecell.cpp
+++ b/ydb/core/scheme/scheme_tablecell.cpp
@@ -198,6 +198,37 @@ bool TSerializedCellVec::DoTryParse(const TString& data) {
     return TryDeserializeCellVec(data, Buf, Cells);
 }
 
+void TCellsStorage::Reset(TArrayRef<const TCell> cells)
+{
+    size_t cellsSize = cells.size();
+    size_t cellsDataSize = sizeof(TCell) * cellsSize;
+
+    for (size_t i = 0; i < cellsSize; ++i) {
+        const auto & cell = cells[i];
+        if (!cell.IsNull() && !cell.IsInline() && cell.Size() != 0) {
+            cellsDataSize += AlignUp(static_cast<size_t>(cell.Size()));
+        }
+    }
+
+    CellsData.resize(cellsDataSize);
+
+    char *cellsData = CellsData.data();
+    Cells = TArrayRef<TCell>{reinterpret_cast<TCell *>(cellsData), cellsSize};
+    cellsData += sizeof(TCell) * cellsSize;
+
+    for (size_t i = 0; i < cellsSize; ++i) {
+        const auto & cell = cells[i];
+
+        if (!cell.IsNull() && !cell.IsInline() && cell.Size() != 0) {
+            memcpy(cellsData, cell.Data(), cell.Size());
+            Cells[i] = TCell(cellsData, cell.Size());
+            cellsData += AlignUp(static_cast<size_t>(cell.Size()));
+        } else {
+            Cells[i] = cell;
+        }
+    }
+}
+
 TOwnedCellVecBatch::TOwnedCellVecBatch()
     : Pool(std::make_unique<TMemoryPool>(InitialPoolSize)) {
 }
diff --git a/ydb/core/scheme/scheme_tablecell.h b/ydb/core/scheme/scheme_tablecell.h
index 7253f0a777..dd9126fd0d 100644
--- a/ydb/core/scheme/scheme_tablecell.h
+++ b/ydb/core/scheme/scheme_tablecell.h
@@ -551,6 +551,22 @@ private:
     TVector<TCell> Cells;
 };
 
+class TCellsStorage
+{
+public:
+    TCellsStorage() = default;
+
+    inline TConstArrayRef<TCell> GetCells() const {
+        return Cells;
+    }
+
+    void Reset(TArrayRef<const TCell> cells);
+
+private:
+    TArrayRef<TCell> Cells;
+    std::vector<char> CellsData;
+};
+
 class TOwnedCellVecBatch {
 public:
     TOwnedCellVecBatch();
diff --git a/ydb/core/tablet_flat/flat_stat_table.h b/ydb/core/tablet_flat/flat_stat_table.h
index 52c5b476fd..98658d720b 100644
--- a/ydb/core/tablet_flat/flat_stat_table.h
+++ b/ydb/core/tablet_flat/flat_stat_table.h
@@ -7,6 +7,8 @@
 #include <util/generic/queue.h>
 #include <util/generic/hash_set.h>
 
+#include <ydb/core/scheme/scheme_tablecell.h>
+
 namespace NKikimr {
 namespace NTable {
 
@@ -29,13 +31,15 @@ public:
         ui64 lastRowCount = stats.RowCount;
         ui64 lastDataSize = stats.DataSize.Size;
 
+        TCellsStorage cellsStorage;
+
         while (!Heap.empty()) {
             TScreenedPartIndexIterator* it = Heap.top();
             Heap.pop();
 
             // makes key copy
-            TSerializedCellVec serialized = TSerializedCellVec(TSerializedCellVec::Serialize({it->GetCurrentKey().Columns, it->GetCurrentKey().ColumnCount}));
-            TDbTupleRef key(KeyColumns->BasicTypes().data(), serialized.GetCells().data(), serialized.GetCells().size());
+            cellsStorage.Reset({it->GetCurrentKey().Columns, it->GetCurrentKey().ColumnCount});
+            TDbTupleRef key(KeyColumns->BasicTypes().data(), cellsStorage.GetCells().data(), cellsStorage.GetCells().size());
 
             auto ready = it->Next(stats);
             if (ready == EReady::Page) {
diff --git a/ydb/core/tx/datashard/datashard__read_iterator.cpp b/ydb/core/tx/datashard/datashard__read_iterator.cpp
index 67017d540d..9deccda5da 100644
--- a/ydb/core/tx/datashard/datashard__read_iterator.cpp
+++ b/ydb/core/tx/datashard/datashard__read_iterator.cpp
@@ -46,48 +46,6 @@ private:
     }
 };
 
-class TCellsStorage
-{
-public:
-    TCellsStorage() = default;
-
-    void Reset(TArrayRef<const TCell> cells)
-    {
-        size_t CellsSize = cells.size();
-        Cells.resize(CellsSize);
-
-        size_t cellsDataSize = 0;
-        for (size_t i = 0; i < CellsSize; ++i) {
-            auto cell = cells[i];
-            Cells[i] = cell;
-
-            if (!cell.IsNull() && !cell.IsInline() && cell.Size() != 0) {
-                cellsDataSize += cell.Size();
-            }
-        }
-
-        CellsData.resize(cellsDataSize);
-        char *cellsData = CellsData.data();
-
-        for (size_t i = 0; i < CellsSize; ++i) {
-            auto cell = Cells[i];
-
-            if (!cell.IsNull() && !cell.IsInline() && cell.Size() != 0) {
-                memcpy(cellsData, cell.Data(), cell.Size());
-                Cells[i] = TCell(cellsData, cell.Size());
-                cellsData += cell.Size();
-            }
-        }
-    }
-
-    TArrayRef<const TCell> GetCells() const {
-        return Cells;
-    }
-private:
-    TSmallVec<TCell> Cells;
-    std::vector<char> CellsData;
-};
-
 class TCellBlockBuilder : public IBlockBuilder {
 public:
     bool Start(