From 86a18dc46aae3a4a6410e3f3d864fa0ec4e5b2cd Mon Sep 17 00:00:00 2001
From: Igor Gumenyuk <me@exslim.net>
Date: Fri, 15 Sep 2017 17:00:12 +0300
Subject: [PATCH] Fixed #28334 -- Added caching for hstore/citext OIDs.

---
 django/contrib/postgres/operations.py | 10 ++++++-
 django/contrib/postgres/signals.py    | 40 +++++++++++++++++++++++----
 tests/postgres_tests/test_signals.py  | 33 ++++++++++++++++++++++
 3 files changed, 76 insertions(+), 7 deletions(-)
 create mode 100644 tests/postgres_tests/test_signals.py

diff --git a/django/contrib/postgres/operations.py b/django/contrib/postgres/operations.py
index be9ed9cb23..95e7edcdea 100644
--- a/django/contrib/postgres/operations.py
+++ b/django/contrib/postgres/operations.py
@@ -1,4 +1,6 @@
-from django.contrib.postgres.signals import register_type_handlers
+from django.contrib.postgres.signals import (
+    get_citext_oids, get_hstore_oids, register_type_handlers,
+)
 from django.db.migrations.operations.base import Operation
 
 
@@ -15,6 +17,9 @@ class CreateExtension(Operation):
         if schema_editor.connection.vendor != 'postgresql':
             return
         schema_editor.execute("CREATE EXTENSION IF NOT EXISTS %s" % schema_editor.quote_name(self.name))
+        # Clear cached, stale oids.
+        get_hstore_oids.cache_clear()
+        get_citext_oids.cache_clear()
         # Registering new type handlers cannot be done before the extension is
         # installed, otherwise a subsequent data migration would use the same
         # connection.
@@ -22,6 +27,9 @@ class CreateExtension(Operation):
 
     def database_backwards(self, app_label, schema_editor, from_state, to_state):
         schema_editor.execute("DROP EXTENSION %s" % schema_editor.quote_name(self.name))
+        # Clear cached, stale oids.
+        get_hstore_oids.cache_clear()
+        get_citext_oids.cache_clear()
 
     def describe(self):
         return "Creates extension %s" % self.name
diff --git a/django/contrib/postgres/signals.py b/django/contrib/postgres/signals.py
index 4ffc90c213..079aafe9c8 100644
--- a/django/contrib/postgres/signals.py
+++ b/django/contrib/postgres/signals.py
@@ -1,14 +1,45 @@
+import functools
+
 import psycopg2
 from psycopg2 import ProgrammingError
 from psycopg2.extras import register_hstore
 
+from django.db import connections
+
+
+@functools.lru_cache()
+def get_hstore_oids(connection_alias):
+    """Return hstore and hstore array OIDs."""
+    with connections[connection_alias].cursor() as cursor:
+        cursor.execute(
+            "SELECT t.oid, typarray "
+            "FROM pg_type t "
+            "JOIN pg_namespace ns ON typnamespace = ns.oid "
+            "WHERE typname = 'hstore'"
+        )
+        oids = []
+        array_oids = []
+        for row in cursor:
+            oids.append(row[0])
+            array_oids.append(row[1])
+        return tuple(oids), tuple(array_oids)
+
+
+@functools.lru_cache()
+def get_citext_oids(connection_alias):
+    """Return citext array OIDs."""
+    with connections[connection_alias].cursor() as cursor:
+        cursor.execute("SELECT typarray FROM pg_type WHERE typname = 'citext'")
+        return tuple(row[0] for row in cursor)
+
 
 def register_type_handlers(connection, **kwargs):
     if connection.vendor != 'postgresql':
         return
 
     try:
-        register_hstore(connection.connection, globally=True)
+        oids, array_oids = get_hstore_oids(connection.alias)
+        register_hstore(connection.connection, globally=True, oid=oids, array_oid=array_oids)
     except ProgrammingError:
         # Hstore is not available on the database.
         #
@@ -21,11 +52,8 @@ def register_type_handlers(connection, **kwargs):
         pass
 
     try:
-        with connection.cursor() as cursor:
-            # Retrieve oids of citext arrays.
-            cursor.execute("SELECT typarray FROM pg_type WHERE typname = 'citext'")
-            oids = tuple(row[0] for row in cursor)
-        array_type = psycopg2.extensions.new_array_type(oids, 'citext[]', psycopg2.STRING)
+        citext_oids = get_citext_oids(connection.alias)
+        array_type = psycopg2.extensions.new_array_type(citext_oids, 'citext[]', psycopg2.STRING)
         psycopg2.extensions.register_type(array_type, None)
     except ProgrammingError:
         # citext is not available on the database.
diff --git a/tests/postgres_tests/test_signals.py b/tests/postgres_tests/test_signals.py
new file mode 100644
index 0000000000..a7112f014c
--- /dev/null
+++ b/tests/postgres_tests/test_signals.py
@@ -0,0 +1,33 @@
+from django.db import connection
+
+from . import PostgreSQLTestCase
+
+try:
+    from django.contrib.postgres.signals import get_hstore_oids, get_citext_oids
+except ImportError:
+    pass  # pyscogp2 isn't installed.
+
+
+class OIDTests(PostgreSQLTestCase):
+
+    def assertOIDs(self, oids):
+        self.assertIsInstance(oids, tuple)
+        self.assertGreater(len(oids), 0)
+        self.assertTrue(all(isinstance(oid, int) for oid in oids))
+
+    def test_hstore_cache(self):
+        with self.assertNumQueries(0):
+            get_hstore_oids(connection.alias)
+
+    def test_citext_cache(self):
+        with self.assertNumQueries(0):
+            get_citext_oids(connection.alias)
+
+    def test_hstore_values(self):
+        oids, array_oids = get_hstore_oids(connection.alias)
+        self.assertOIDs(oids)
+        self.assertOIDs(array_oids)
+
+    def test_citext_values(self):
+        oids = get_citext_oids(connection.alias)
+        self.assertOIDs(oids)