app/django/core/cache/backends/db.py
author Pawel Solyga <Pawel.Solyga@gmail.com>
Tue, 14 Oct 2008 16:00:59 +0000
changeset 323 ff1a9aa48cfd
parent 54 03e267d67478
permissions -rw-r--r--
Load ../vendor/django into trunk/app/django.
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"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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        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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            return False
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        else:
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            transaction.commit_unless_managed()
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            return True
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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]])