diff --git a/dbms/include/DB/Interpreters/sortBlock.h b/dbms/include/DB/Interpreters/sortBlock.h
index 9026611be5e..341cc076bef 100644
--- a/dbms/include/DB/Interpreters/sortBlock.h
+++ b/dbms/include/DB/Interpreters/sortBlock.h
@@ -23,4 +23,10 @@ void stableSortBlock(Block & block, const SortDescription & description);
   */
 void stableGetPermutation(const Block & block, const SortDescription & description, IColumn::Permutation & out_permutation);
 
+
+/** Быстро проверить, является ли блок уже отсортированным. Если блок не отсортирован - возвращает false максимально быстро.
+  * Не поддерживаются collations.
+  */
+bool isAlreadySorted(const Block & block, const SortDescription & description);
+
 }
diff --git a/dbms/src/Interpreters/sortBlock.cpp b/dbms/src/Interpreters/sortBlock.cpp
index aebc60ff1ea..f0c090d61ef 100644
--- a/dbms/src/Interpreters/sortBlock.cpp
+++ b/dbms/src/Interpreters/sortBlock.cpp
@@ -172,6 +172,50 @@ void stableGetPermutation(const Block & block, const SortDescription & descripti
 }
 
 
+bool isAlreadySorted(const Block & block, const SortDescription & description)
+{
+	if (!block)
+		return true;
+
+	size_t rows = block.rows();
+
+	ColumnsWithSortDescriptions columns_with_sort_desc;
+
+	for (size_t i = 0, size = description.size(); i < size; ++i)
+	{
+		const IColumn * column = !description[i].column_name.empty()
+			? block.getByName(description[i].column_name).column
+			: block.getByPosition(description[i].column_number).column;
+
+		columns_with_sort_desc.push_back(std::make_pair(column, description[i]));
+	}
+
+	PartialSortingLess less(columns_with_sort_desc);
+
+	/** Если строк не слишком мало, то предпримем быструю попытку проверить, что блок не сортирован.
+	  * Константы - наугад.
+	  */
+	static constexpr size_t num_rows_to_try = 10;
+	if (rows > num_rows_to_try * 5)
+	{
+		for (size_t i = 1; i < num_rows_to_try; ++i)
+		{
+			size_t prev_position = rows * (i - 1) / num_rows_to_try;
+			size_t curr_position = rows * i / num_rows_to_try;
+
+			if (less(curr_position, prev_position))
+				return false;
+		}
+	}
+
+	for (size_t i = 1; i < rows; ++i)
+		if (less(i, i - 1))
+			return false;
+
+	return true;
+}
+
+
 void stableSortBlock(Block & block, const SortDescription & description)
 {
 	if (!block)
diff --git a/dbms/src/Storages/MergeTree/MergeTreeDataWriter.cpp b/dbms/src/Storages/MergeTree/MergeTreeDataWriter.cpp
index 081179c4ba4..83ebb71cca2 100644
--- a/dbms/src/Storages/MergeTree/MergeTreeDataWriter.cpp
+++ b/dbms/src/Storages/MergeTree/MergeTreeDataWriter.cpp
@@ -109,8 +109,11 @@ MergeTreeData::MutableDataPartPtr MergeTreeDataWriter::writeTempPart(BlockWithDa
 	IColumn::Permutation perm;
 	if (data.mode != MergeTreeData::Unsorted)
 	{
-		stableGetPermutation(block, sort_descr, perm);
-		perm_ptr = &perm;
+		if (!isAlreadySorted(block, sort_descr))
+		{
+			stableGetPermutation(block, sort_descr, perm);
+			perm_ptr = &perm;
+		}
 	}
 
 	NamesAndTypesList columns = data.getColumnsList().filter(block.getColumnsList().getNames());