Ticket #15580: 15580.patch

django/core/cache/backends/db.py

@@ -126 +126 @@
         if self._cull_frequency == 0:
             self.clear()
         else:
-            table = connections[db].ops.quote_name(self._table)
+            ops = connections[db].ops
+            table = ops.quote_name(self._table)
             cursor.execute("DELETE FROM %s WHERE expires < %%s" % table,
                            [connections[db].ops.value_to_db_datetime(now)])
             cursor.execute("SELECT COUNT(*) FROM %s" % table)
             num = cursor.fetchone()[0]
             if num > self._max_entries:
-                cursor.execute("SELECT cache_key FROM %s ORDER BY cache_key LIMIT 1 OFFSET %%s" % table, [num / self._cull_frequency])
+                cursor.execute(ops.cache_key_culling_threshold() % table, [num / self._cull_frequency])
                 cursor.execute("DELETE FROM %s WHERE cache_key < %%s" % table, [cursor.fetchone()[0]])
 
     def clear(self):

django/db/backends/__init__.py

@@ -401 +401 @@
         """
         return None
 
+    def cache_key_culling_threshold(self):
+        """
+        Returns a SQL query that retrieves the first cache key greater than the
+        n smallest.
+        
+        This is used by the 'db' cache backend to determine where to start
+        culling.
+        """
+        return "SELECT cache_key FROM %s ORDER BY cache_key LIMIT 1 OFFSET %%s"
+
     def date_extract_sql(self, lookup_type, field_name):
         """
         Given a lookup_type of 'year', 'month' or 'day', returns the SQL that

django/db/backends/oracle/base.py

@@ -111 +111 @@
 /""" % locals()
         return sequence_sql, trigger_sql
 
+    def cache_key_culling_threshold(self):
+        return """SELECT cache_key
+FROM (SELECT cache_key, rank() OVER (ORDER BY cache_key) AS rank FROM %s)
+WHERE rank = %%s + 1"""
+
     def date_extract_sql(self, lookup_type, field_name):
         # http://download-east.oracle.com/docs/cd/B10501_01/server.920/a96540/functions42a.htm#1017163
         if lookup_type == 'week_day':