ignore preferred_max_column_in_block_size_bytes if zero [#CLICKHOUSE-3170]

dbms/src/Storages/MergeTree/MergeTreeBaseBlockInputStream.cpp

@@ -87,13 +87,17 @@ Block MergeTreeBaseBlockInputStream::readFromPart()
         if (!task.size_predictor)
             return max_block_size_rows;
 
-        size_t rows_to_read_for_block = std::max(index_granularity, task.size_predictor->estimateNumRows(preferred_block_size_bytes));
-        size_t rows_to_read_for_max_size_column
-            = task.size_predictor->estimateNumRowsForMaxSizeColumn(preferred_max_column_in_block_size_bytes);
-        double filtration_ratio = std::max(min_filtration_ratio, 1.0 - task.size_predictor->filtered_rows_ratio);
-        size_t rows_to_read_for_max_size_column_with_filtration
-            = static_cast<size_t>(rows_to_read_for_max_size_column / filtration_ratio);
-        size_t rows_to_read = std::min(rows_to_read_for_block, rows_to_read_for_max_size_column_with_filtration);
+        size_t rows_to_read = std::max(index_granularity, task.size_predictor->estimateNumRows(preferred_block_size_bytes));
+
+        if (preferred_max_column_in_block_size_bytes)
+        {
+            size_t rows_to_read_for_max_size_column
+                = task.size_predictor->estimateNumRowsForMaxSizeColumn(preferred_max_column_in_block_size_bytes);
+            double filtration_ratio = std::max(min_filtration_ratio, 1.0 - task.size_predictor->filtered_rows_ratio);
+            size_t rows_to_read_for_max_size_column_with_filtration
+                = static_cast<size_t>(rows_to_read_for_max_size_column / filtration_ratio);
+            rows_to_read = std::min(rows_to_read, rows_to_read_for_max_size_column_with_filtration);
+        }
 
         size_t unread_rows_in_current_granule = reader.unreadRowsInCurrentGranule();
         if (unread_rows_in_current_granule >= rows_to_read)