89 lines
3.7 KiB
Python
89 lines
3.7 KiB
Python
"Database cache backend."
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from django.core.cache.backends.base import BaseCache
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from django.db import connection, transaction, DatabaseError
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import base64, time
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from datetime import datetime
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try:
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import cPickle as pickle
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except ImportError:
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import pickle
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class CacheClass(BaseCache):
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def __init__(self, table, params):
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BaseCache.__init__(self, params)
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self._table = table
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max_entries = params.get('max_entries', 300)
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try:
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self._max_entries = int(max_entries)
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except (ValueError, TypeError):
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self._max_entries = 300
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cull_frequency = params.get('cull_frequency', 3)
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try:
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self._cull_frequency = int(cull_frequency)
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except (ValueError, TypeError):
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self._cull_frequency = 3
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def get(self, key, default=None):
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cursor = connection.cursor()
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cursor.execute("SELECT cache_key, value, expires FROM %s WHERE cache_key = %%s" % self._table, [key])
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row = cursor.fetchone()
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if row is None:
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return default
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now = datetime.now()
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if row[2] < now:
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cursor.execute("DELETE FROM %s WHERE cache_key = %%s" % self._table, [key])
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transaction.commit_unless_managed()
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return default
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return pickle.loads(base64.decodestring(row[1]))
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def set(self, key, value, timeout=None):
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return self._base_set('set', key, value, timeout)
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def add(self, key, value, timeout=None):
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return self._base_set('add', key, value, timeout)
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def _base_set(self, mode, key, value, timeout=None):
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if timeout is None:
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timeout = self.default_timeout
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cursor = connection.cursor()
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cursor.execute("SELECT COUNT(*) FROM %s" % self._table)
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num = cursor.fetchone()[0]
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now = datetime.now().replace(microsecond=0)
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exp = datetime.fromtimestamp(time.time() + timeout).replace(microsecond=0)
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if num > self._max_entries:
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self._cull(cursor, now)
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encoded = base64.encodestring(pickle.dumps(value, 2)).strip()
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cursor.execute("SELECT cache_key FROM %s WHERE cache_key = %%s" % self._table, [key])
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try:
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if mode == 'set' and cursor.fetchone():
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cursor.execute("UPDATE %s SET value = %%s, expires = %%s WHERE cache_key = %%s" % self._table, [encoded, str(exp), key])
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else:
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cursor.execute("INSERT INTO %s (cache_key, value, expires) VALUES (%%s, %%s, %%s)" % self._table, [key, encoded, str(exp)])
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except DatabaseError:
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# To be threadsafe, updates/inserts are allowed to fail silently
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pass
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else:
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transaction.commit_unless_managed()
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def delete(self, key):
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cursor = connection.cursor()
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cursor.execute("DELETE FROM %s WHERE cache_key = %%s" % self._table, [key])
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transaction.commit_unless_managed()
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def has_key(self, key):
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cursor = connection.cursor()
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cursor.execute("SELECT cache_key FROM %s WHERE cache_key = %%s" % self._table, [key])
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return cursor.fetchone() is not None
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def _cull(self, cursor, now):
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if self._cull_frequency == 0:
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cursor.execute("DELETE FROM %s" % self._table)
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else:
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cursor.execute("DELETE FROM %s WHERE expires < %%s" % self._table, [str(now)])
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cursor.execute("SELECT COUNT(*) FROM %s" % self._table)
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num = cursor.fetchone()[0]
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if num > self._max_entries:
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cursor.execute("SELECT cache_key FROM %s ORDER BY cache_key LIMIT 1 OFFSET %%s" % self._table, [num / self._cull_frequency])
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cursor.execute("DELETE FROM %s WHERE cache_key < %%s" % self._table, [cursor.fetchone()[0]])
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