204 lines
8.6 KiB
Python
204 lines
8.6 KiB
Python
"Database cache backend."
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import base64
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from datetime import datetime
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from django.conf import settings
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from django.core.cache.backends.base import DEFAULT_TIMEOUT, BaseCache
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from django.db import DatabaseError, connections, router, transaction
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from django.db.backends.utils import typecast_timestamp
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from django.utils import six, timezone
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from django.utils.encoding import force_bytes
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try:
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from django.utils.six.moves import cPickle as pickle
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except ImportError:
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import pickle
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class Options(object):
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"""A class that will quack like a Django model _meta class.
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This allows cache operations to be controlled by the router
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"""
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def __init__(self, table):
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self.db_table = table
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self.app_label = 'django_cache'
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self.model_name = 'cacheentry'
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self.verbose_name = 'cache entry'
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self.verbose_name_plural = 'cache entries'
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self.object_name = 'CacheEntry'
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self.abstract = False
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self.managed = True
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self.proxy = False
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self.swapped = False
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class BaseDatabaseCache(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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class CacheEntry(object):
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_meta = Options(table)
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self.cache_model_class = CacheEntry
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class DatabaseCache(BaseDatabaseCache):
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# This class uses cursors provided by the database connection. This means
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# it reads expiration values as aware or naive datetimes depending on the
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# value of USE_TZ. They must be compared to aware or naive representations
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# of "now" respectively.
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# But it bypasses the ORM for write operations. As a consequence, aware
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# datetimes aren't made naive for databases that don't support time zones.
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# We work around this problem by always using naive datetimes when writing
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# expiration values, in UTC when USE_TZ = True and in local time otherwise.
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def get(self, key, default=None, version=None):
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key = self.make_key(key, version=version)
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self.validate_key(key)
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db = router.db_for_read(self.cache_model_class)
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table = connections[db].ops.quote_name(self._table)
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with connections[db].cursor() as cursor:
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cursor.execute("SELECT cache_key, value, expires FROM %s "
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"WHERE cache_key = %%s" % 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 = timezone.now()
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expires = row[2]
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if connections[db].features.needs_datetime_string_cast and not isinstance(expires, datetime):
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# Note: typecasting is needed by some 3rd party database backends.
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# All core backends work without typecasting, so be careful about
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# changes here - test suite will NOT pick regressions here.
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expires = typecast_timestamp(str(expires))
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if expires < now:
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db = router.db_for_write(self.cache_model_class)
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with connections[db].cursor() as cursor:
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cursor.execute("DELETE FROM %s "
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"WHERE cache_key = %%s" % table, [key])
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return default
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value = connections[db].ops.process_clob(row[1])
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return pickle.loads(base64.b64decode(force_bytes(value)))
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def set(self, key, value, timeout=DEFAULT_TIMEOUT, version=None):
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key = self.make_key(key, version=version)
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self.validate_key(key)
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self._base_set('set', key, value, timeout)
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def add(self, key, value, timeout=DEFAULT_TIMEOUT, version=None):
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key = self.make_key(key, version=version)
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self.validate_key(key)
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return self._base_set('add', key, value, timeout)
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def _base_set(self, mode, key, value, timeout=DEFAULT_TIMEOUT):
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timeout = self.get_backend_timeout(timeout)
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db = router.db_for_write(self.cache_model_class)
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table = connections[db].ops.quote_name(self._table)
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with connections[db].cursor() as cursor:
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cursor.execute("SELECT COUNT(*) FROM %s" % table)
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num = cursor.fetchone()[0]
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now = timezone.now()
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now = now.replace(microsecond=0)
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if timeout is None:
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exp = datetime.max
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elif settings.USE_TZ:
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exp = datetime.utcfromtimestamp(timeout)
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else:
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exp = datetime.fromtimestamp(timeout)
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exp = exp.replace(microsecond=0)
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if num > self._max_entries:
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self._cull(db, cursor, now)
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pickled = pickle.dumps(value, pickle.HIGHEST_PROTOCOL)
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b64encoded = base64.b64encode(pickled)
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# The DB column is expecting a string, so make sure the value is a
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# string, not bytes. Refs #19274.
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if six.PY3:
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b64encoded = b64encoded.decode('latin1')
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try:
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# Note: typecasting for datetimes is needed by some 3rd party
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# database backends. All core backends work without typecasting,
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# so be careful about changes here - test suite will NOT pick
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# regressions.
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with transaction.atomic(using=db):
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cursor.execute("SELECT cache_key, expires FROM %s "
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"WHERE cache_key = %%s" % table, [key])
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result = cursor.fetchone()
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if result:
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current_expires = result[1]
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if (connections[db].features.needs_datetime_string_cast and not
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isinstance(current_expires, datetime)):
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current_expires = typecast_timestamp(str(current_expires))
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exp = connections[db].ops.value_to_db_datetime(exp)
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if result and (mode == 'set' or (mode == 'add' and current_expires < now)):
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cursor.execute("UPDATE %s SET value = %%s, expires = %%s "
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"WHERE cache_key = %%s" % table,
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[b64encoded, exp, key])
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else:
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cursor.execute("INSERT INTO %s (cache_key, value, expires) "
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"VALUES (%%s, %%s, %%s)" % table,
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[key, b64encoded, 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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return True
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def delete(self, key, version=None):
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key = self.make_key(key, version=version)
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self.validate_key(key)
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db = router.db_for_write(self.cache_model_class)
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table = connections[db].ops.quote_name(self._table)
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with connections[db].cursor() as cursor:
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cursor.execute("DELETE FROM %s WHERE cache_key = %%s" % table, [key])
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def has_key(self, key, version=None):
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key = self.make_key(key, version=version)
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self.validate_key(key)
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db = router.db_for_read(self.cache_model_class)
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table = connections[db].ops.quote_name(self._table)
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if settings.USE_TZ:
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now = datetime.utcnow()
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else:
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now = datetime.now()
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now = now.replace(microsecond=0)
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with connections[db].cursor() as cursor:
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cursor.execute("SELECT cache_key FROM %s "
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"WHERE cache_key = %%s and expires > %%s" % table,
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[key, connections[db].ops.value_to_db_datetime(now)])
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return cursor.fetchone() is not None
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def _cull(self, db, cursor, now):
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if self._cull_frequency == 0:
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self.clear()
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else:
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# When USE_TZ is True, 'now' will be an aware datetime in UTC.
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now = now.replace(tzinfo=None)
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table = connections[db].ops.quote_name(self._table)
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cursor.execute("DELETE FROM %s WHERE expires < %%s" % table,
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[connections[db].ops.value_to_db_datetime(now)])
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cursor.execute("SELECT COUNT(*) FROM %s" % table)
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num = cursor.fetchone()[0]
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if num > self._max_entries:
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cull_num = num // self._cull_frequency
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cursor.execute(
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connections[db].ops.cache_key_culling_sql() % table,
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[cull_num])
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cursor.execute("DELETE FROM %s "
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"WHERE cache_key < %%s" % table,
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[cursor.fetchone()[0]])
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def clear(self):
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db = router.db_for_write(self.cache_model_class)
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table = connections[db].ops.quote_name(self._table)
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with connections[db].cursor() as cursor:
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cursor.execute('DELETE FROM %s' % table)
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