| "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]]) |