Address comments

src/Processors/Formats/Impl/NativeORCBlockInputFormat.h

@@ -75,7 +75,7 @@ private:
     std::list<UInt64> include_indices;
 
     BlockMissingValues block_missing_values;
-    size_t approx_bytes_read_for_chunk;
+    size_t approx_bytes_read_for_chunk = 0;
 
     const FormatSettings format_settings;
     const std::unordered_set<int> & skip_stripes;

src/Processors/Formats/Impl/ParquetBlockInputFormat.cpp

@@ -645,13 +645,7 @@ Chunk ParquetBlockInputFormat::generate()
         return {};
 
     if (need_only_count)
-    {
-        auto & row_group_batch = row_group_batches[row_group_batches_completed++];
-        size_t num_rows = 0;
-        for (int row_group_index : row_group_batch.row_groups_idxs)
-            num_rows += metadata->RowGroup(row_group_index)->num_rows();
-        return getChunkForCount(num_rows);
-    }
+        return getChunkForCount(row_group_batches[row_group_batches_completed++].total_rows);
 
     std::unique_lock lock(mutex);
 

src/Storages/IStorage.h

@@ -254,7 +254,8 @@ public:
     /// because those are internally translated into 'ALTER UDPATE' mutations.
     virtual bool supportsDelete() const { return false; }
 
-    /// Return true if the trivial count query could be optimized without reading the data at all.
+    /// Return true if the trivial count query could be optimized without reading the data at all
+    /// in totalRows() or totalRowsByPartitionPredicate() methods or with optimized reading in read() method.
     virtual bool supportsTrivialCountOptimization() const { return false; }
 
 private:

tests/performance/count_from_formats.xml

@@ -38,7 +38,6 @@
             <value>CapnProto</value>
             <value>ORC</value>
             <value>Parquet</value>
-            <value>Arrow</value>
         </values>
     </substitution>
 </substitutions>