1 files changed, 89 insertions, 0 deletions
diff --git a/webapp/django/core/cache/backends/db.py b/webapp/django/core/cache/backends/db.py
new file mode 100644
index 0000000000..d2b422af83
--- /dev/null
+++ b/webapp/django/core/cache/backends/db.py
@@ -0,0 +1,89 @@
+"Database cache backend."
+
+from django.core.cache.backends.base import BaseCache
+from django.db import connection, transaction, DatabaseError
+import base64, time
+from datetime import datetime
+try:
+    import cPickle as pickle
+except ImportError:
+    import pickle
+
+class CacheClass(BaseCache):
+    def __init__(self, table, params):
+        BaseCache.__init__(self, params)
+        self._table = table
+        max_entries = params.get('max_entries', 300)
+        try:
+            self._max_entries = int(max_entries)
+        except (ValueError, TypeError):
+            self._max_entries = 300
+        cull_frequency = params.get('cull_frequency', 3)
+        try:
+            self._cull_frequency = int(cull_frequency)
+        except (ValueError, TypeError):
+            self._cull_frequency = 3
+
+    def get(self, key, default=None):
+        cursor = connection.cursor()
+        cursor.execute("SELECT cache_key, value, expires FROM %s WHERE cache_key = %%s" % self._table, [key])
+        row = cursor.fetchone()
+        if row is None:
+            return default
+        now = datetime.now()
+        if row[2] < now:
+            cursor.execute("DELETE FROM %s WHERE cache_key = %%s" % self._table, [key])
+            transaction.commit_unless_managed()
+            return default
+        return pickle.loads(base64.decodestring(row[1]))
+
+    def set(self, key, value, timeout=None):
+        self._base_set('set', key, value, timeout)
+
+    def add(self, key, value, timeout=None):
+        return self._base_set('add', key, value, timeout)
+
+    def _base_set(self, mode, key, value, timeout=None):
+        if timeout is None:
+            timeout = self.default_timeout
+        cursor = connection.cursor()
+        cursor.execute("SELECT COUNT(*) FROM %s" % self._table)
+        num = cursor.fetchone()[0]
+        now = datetime.now().replace(microsecond=0)
+        exp = datetime.fromtimestamp(time.time() + timeout).replace(microsecond=0)
+        if num > self._max_entries:
+            self._cull(cursor, now)
+        encoded = base64.encodestring(pickle.dumps(value, 2)).strip()
+        cursor.execute("SELECT cache_key FROM %s WHERE cache_key = %%s" % self._table, [key])
+        try:
+            if mode == 'set' and cursor.fetchone():
+                cursor.execute("UPDATE %s SET value = %%s, expires = %%s WHERE cache_key = %%s" % self._table, [encoded, str(exp), key])
+            else:
+                cursor.execute("INSERT INTO %s (cache_key, value, expires) VALUES (%%s, %%s, %%s)" % self._table, [key, encoded, str(exp)])
+        except DatabaseError:
+            # To be threadsafe, updates/inserts are allowed to fail silently
+            return False
+        else:
+            transaction.commit_unless_managed()
+            return True
+
+    def delete(self, key):
+        cursor = connection.cursor()
+        cursor.execute("DELETE FROM %s WHERE cache_key = %%s" % self._table, [key])
+        transaction.commit_unless_managed()
+
+    def has_key(self, key):
+        cursor = connection.cursor()
+        cursor.execute("SELECT cache_key FROM %s WHERE cache_key = %%s" % self._table, [key])
+        return cursor.fetchone() is not None
+
+    def _cull(self, cursor, now):
+        if self._cull_frequency == 0:
+            cursor.execute("DELETE FROM %s" % self._table)
+        else:
+            cursor.execute("DELETE FROM %s WHERE expires < %%s" % self._table, [str(now)])
+            cursor.execute("SELECT COUNT(*) FROM %s" % self._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" % self._table, [num / self._cull_frequency])
+                cursor.execute("DELETE FROM %s WHERE cache_key < %%s" % self._table, [cursor.fetchone()[0]])