diff --git a/dbms/src/Storages/tests/active_parts.py b/dbms/src/Storages/tests/active_parts.py
index 61ce2c7c23e..cd07bc3b935 100644
--- a/dbms/src/Storages/tests/active_parts.py
+++ b/dbms/src/Storages/tests/active_parts.py
@@ -3,30 +3,42 @@
 
 # Выводит список активных кусков - кусков, не покрытых никаким другим куском.
 # Использование: `ls /opt/clickhouse/data/merge/visits | active_parts.py`
+# TODO: O(N^2) -> O(N log N)
 
 import sys
 import re
 
 parts = {}
 for s in sys.stdin.read().split():
-        m = re.match('^([0-9]{6})[0-9]{2}_([0-9]{6})[0-9]{2}_([0-9]+)_([0-9]+)_([0-9]+)$', s)
-        if m == None:
-                continue
-        m1 = m.group(1)
-        m2 = m.group(2)
-        i1 = int(m.group(3))
-        i2 = int(m.group(4))
-        l = int(m.group(5))
-        if m1 != m2:
-                raise Exception('not in single month: ' + s)
-        if m1 not in parts:
-                parts[m1] = []
-        parts[m1].append((i1, i2, l, s))
+	m = re.match('^([0-9]{6})[0-9]{2}_([0-9]{6})[0-9]{2}_([0-9]+)_([0-9]+)_([0-9]+)$', s)
+	if m == None:
+		continue
+	m1 = m.group(1)
+	m2 = m.group(2)
+	i1 = int(m.group(3))
+	i2 = int(m.group(4))
+	l = int(m.group(5))
+	if m1 != m2:
+		raise Exception('not in single month: ' + s)
+	if m1 not in parts:
+		parts[m1] = []
+	parts[m1].append((i1, i2, l, s))
 
 for m in parts:
-        for x1, y1, l1, s1 in parts[m]:
-                for x2, y2, l2, s2 in parts[m]:
-                        if x1 >= x2 and y1 <= y2 and l1 < l2:
-                                break
-                else:
-                        print s1
+	for x1, y1, l1, s1 in parts[m]:
+		contained = False
+		for x2, y2, l2, s2 in parts[m]:
+			if x1 >= x2 and y1 <= y2 and l1 < l2: # 2 contains 1
+				contained = True
+				continue
+			if x1 <= x2 and y1 >= y2 and l1 > l2: # 1 contains 2
+				continue
+			if x1 == x1 and y1 == y2 and l1 == l2: # 1 and 2 coincide
+				continue
+			if x1 > y2: # 1 is to the right of 2
+				continue
+			if x2 > y1: # 2 is to the right of 1
+				continue
+			raise Exception('invalid parts intersection: ' + s1 + ' and ' + s2)
+		if not contained:
+			print s1