fix reading logic in case memory control (#11768)

Author: ivanmorozov333

ydb/core/tx/columnshard/engines/reader/plain_reader/iterator/source.h

@@ -75,6 +75,7 @@ class IDataSource {
     virtual bool DoStartFetchingAccessor(const std::shared_ptr<IDataSource>& sourcePtr, const TFetchingScriptCursor& step) = 0;
 
 public:
+    virtual bool NeedAccessorsForRead() const = 0;
     virtual bool NeedAccessorsFetching() const = 0;
 
     bool StartFetchingAccessor(const std::shared_ptr<IDataSource>& sourcePtr, const TFetchingScriptCursor& step) {
@@ -110,7 +111,7 @@ class IDataSource {
     void SetSourceInMemory(const bool value) {
         AFL_VERIFY(!IsSourceInMemoryFlag);
         IsSourceInMemoryFlag = value;
-        if (NeedAccessorsFetching()) {
+        if (NeedAccessorsForRead()) {
             AFL_VERIFY(StageData);
             if (!value) {
                 StageData->SetUseFilter(value);
@@ -317,6 +318,10 @@ class TPortionDataSource: public IDataSource {
     virtual bool DoStartFetchingAccessor(const std::shared_ptr<IDataSource>& sourcePtr, const TFetchingScriptCursor& step) override;
 
 public:
+    virtual bool NeedAccessorsForRead() const override {
+        return true;
+    }
+
     virtual bool NeedAccessorsFetching() const override {
         return !StageData  || !StageData->HasPortionAccessor();
     }
@@ -425,6 +430,10 @@ class TCommittedDataSource: public IDataSource {
     }
 
 public:
+    virtual bool NeedAccessorsForRead() const override {
+        return false;
+    }
+
     virtual bool NeedAccessorsFetching() const override {
         return false;
     }