test: add perf test for references

frappe/tests/test_perf.py

@@ -16,6 +16,8 @@ query. This test can be written like this.
 >>> 		get_controller("User")
 
 """
+import gc
+import sys
 import time
 from unittest.mock import patch
 
@@ -176,3 +178,18 @@ class TestPerformance(FrappeTestCase):
 		query = frappe.get_all("DocType", {"autoname": ("is", "set")}, run=0).lower()
 		self.assertNotIn("coalesce", query)
 		self.assertNotIn("ifnull", query)
+
+	def test_no_stale_ref_sql(self):
+		"""frappe.db.sql should not hold any internal references to result set.
+
+		pymysql stores results internally. If your code reads a lot and doesn't make another
+		query, for that entire duration there's copy of result consuming memory in internal
+		attributes of pymysql.
+		We clear it manually, this test ensures that it actually works.
+		"""
+
+		query = "select * from tabUser"
+		for kwargs in ({}, {"as_dict": True}, {"as_list": True}):
+			result = frappe.db.sql(query, **kwargs)
+			self.assertEqual(sys.getrefcount(result), 2)  # Note: This always returns +1
+			self.assertFalse(gc.get_referrers(result))