Datashard part iterator improve performance

Datashard part iterator improve performance

Pull Request resolved: #294

1 files changed, 18 insertions, 12 deletions

diff --git a/ydb/core/tablet_flat/flat_part_iter_multi.h b/ydb/core/tablet_flat/flat_part_iter_multi.h
index ae1e04ca4e5..972b7810095 100644
--- a/ydb/core/tablet_flat/flat_part_iter_multi.h
+++ b/ydb/core/tablet_flat/flat_part_iter_multi.h
@@ -679,8 +679,6 @@ namespace NTable {
             , SkipMainVersion(false)
             , SkipEraseVersion(false)
         {
-            Key.reserve(KeyCellDefaults->Size());
-
             Groups.reserve(Pinout.AltGroups().size());
             GroupRemap.resize(Part->Scheme->Groups.size(), Max<ui32>());
 
@@ -690,6 +688,14 @@ namespace NTable {
                 Groups.emplace_back(Part->GetGroupIndex(groupId), groupId);
                 GroupRemap[group] = idx;
             }
+
+            size_t KeyCellDefaultsSize = KeyCellDefaults->Size();
+            Key.resize(KeyCellDefaultsSize);
+
+            size_t infoSize = Part->Scheme->Groups[0].ColsKeyData.size();
+            for (size_t pos = infoSize; pos < KeyCellDefaultsSize; ++pos) {
+                Key[pos] = (*KeyCellDefaults)[pos];
+            }
         }
 
         void ClearBounds() noexcept
@@ -1133,7 +1139,7 @@ namespace NTable {
     private:
         Y_FORCE_INLINE void ClearKey() noexcept
         {
-            Key.clear();
+            KeyInitialized = false;
             SkipMainDeltas = 0;
             SkipMainVersion = false;
             SkipEraseVersion = false;
@@ -1142,17 +1148,16 @@ namespace NTable {
         Y_FORCE_INLINE void InitKey() const noexcept
         {
             Y_VERIFY_DEBUG(Main.IsValid(), "Attempt to get an invalid key");
+            if (KeyInitialized)
+                return;
 
-            if (!Key) {
-                auto& info = Part->Scheme->Groups[0].ColsKeyData;
-
-                for (size_t pos = 0; pos < info.size(); ++pos) {
-                    Key.push_back(Main.GetRecord()->Cell(info[pos]));
-                }
+            KeyInitialized = true;
 
-                for (size_t pos = info.size(); pos < KeyCellDefaults->Size(); ++pos) {
-                    Key.push_back((*KeyCellDefaults)[pos]);
-                }
+            auto it = Key.begin();
+            auto* record = Main.GetRecord();
+            for (auto & info : Part->Scheme->Groups[0].ColsKeyData) {
+                *it = record->Cell(info);
+                ++it;
             }
         }
 
@@ -1247,6 +1252,7 @@ namespace NTable {
         mutable TSmallVec<TPartGroupRowIt> Groups;
 
         // Key is lazily initialized so needs to be mutable
+        mutable bool KeyInitialized = false;
         mutable TSmallVec<TCell> Key;
 
         // History state is used when we need to position into history data