Optional columns feature flags (#7814)

 Conflicts:
	ydb/core/protos/feature_flags.proto
	ydb/core/tx/columnshard/engines/scheme/versions/abstract_scheme.cpp

Author: ivanmorozov333

ydb/core/formats/arrow/modifier/subset.h

@@ -14,6 +14,12 @@ class TSchemaSubset {
     TSchemaSubset() = default;
     TSchemaSubset(const std::set<ui32>& fieldsIdx, const ui32 fieldsCount);
 
+    static TSchemaSubset AllFieldsAccepted() {
+        TSchemaSubset result;
+        result.Exclude = true;
+        return result;
+    }
+
     template <class T>
     std::vector<T> Apply(const std::vector<T>& fullSchema) const {
         if (FieldIdx.empty()) {

ydb/core/protos/feature_flags.proto

@@ -146,4 +146,6 @@ message TFeatureFlags {
     optional bool EnableSingleCompositeActionGroup = 131 [default = false];
     optional bool EnableResourcePoolsOnServerless = 132 [default = false];
     optional bool EnableChangefeedsOnIndexTables = 134 [default = false];
+    optional bool EnableResourcePoolsCounters = 135 [default = false];
+    optional bool EnableOptionalColumnsInColumnShard = 136 [default = false];
 }

ydb/core/tx/columnshard/engines/scheme/versions/abstract_scheme.cpp

@@ -53,6 +53,8 @@ TConclusion<std::shared_ptr<NArrow::TGeneralContainer>> ISnapshotSchema::Normali
             }
         }
         if (restoreColumnIds.contains(columnId)) {
+            AFL_VERIFY(!!GetExternalDefaultValueVerified(columnId) || GetIndexInfo().IsNullableVerified(columnId))("column_name",
+                                                                          GetIndexInfo().GetColumnName(columnId, false))("id", columnId);
             result->AddField(resultField,
                     NArrow::TThreadSimpleArraysCache::Get(resultField->type(), GetExternalDefaultValueVerified(columnId), batch->num_rows()))
                 .Validate();
@@ -114,8 +116,9 @@ TConclusion<std::shared_ptr<arrow::RecordBatch>> ISnapshotSchema::PrepareForModi
     Y_DEBUG_ABORT_UNLESS(NArrow::IsSortedAndUnique(batch, GetIndexInfo().GetPrimaryKey()));
 
     switch (mType) {
+        case NEvWrite::EModificationType::Replace:
         case NEvWrite::EModificationType::Upsert: {
-            AFL_VERIFY(batch->num_columns() <= dstSchema->num_fields());
+                AFL_VERIFY(batch->num_columns() <= dstSchema->num_fields());
             if (batch->num_columns() < dstSchema->num_fields()) {
                 for (auto&& f : dstSchema->fields()) {
                     if (GetIndexInfo().IsNullableVerified(f->name())) {
@@ -132,7 +135,6 @@ TConclusion<std::shared_ptr<arrow::RecordBatch>> ISnapshotSchema::PrepareForModi
             return batch;
         }
         case NEvWrite::EModificationType::Delete:
-        case NEvWrite::EModificationType::Replace:
         case NEvWrite::EModificationType::Insert:
         case NEvWrite::EModificationType::Update:
             return batch;

ydb/core/tx/columnshard/operations/slice_builder/builder.cpp

@@ -55,7 +55,14 @@ TConclusionStatus TBuildSlicesTask::DoExecute(const std::shared_ptr<ITask>& /*ta
     if (OriginalBatch->num_columns() != indexSchema->num_fields()) {
         AFL_VERIFY(OriginalBatch->num_columns() < indexSchema->num_fields())("original", OriginalBatch->num_columns())(
                                                       "index", indexSchema->num_fields());
-
+        if (HasAppData() && !AppDataVerified().FeatureFlags.GetEnableOptionalColumnsInColumnShard()) {
+            subset = NArrow::TSchemaSubset::AllFieldsAccepted();
+            const std::vector<ui32>& columnIdsVector = ActualSchema->GetIndexInfo().GetColumnIds(false);
+            const std::set<ui32> columnIdsSet(columnIdsVector.begin(), columnIdsVector.end());
+            auto normalized =
+                ActualSchema->NormalizeBatch(*ActualSchema, std::make_shared<NArrow::TGeneralContainer>(OriginalBatch), columnIdsSet).DetachResult();
+            OriginalBatch = NArrow::ToBatch(normalized->BuildTableVerified(), true);
+        }
     }
     WriteData.MutableWriteMeta().SetWriteMiddle2StartInstant(TMonotonic::Now());
     auto batches = BuildSlices();