186 lines
6.8 KiB
Python
186 lines
6.8 KiB
Python
"Memcached cache backend"
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import pickle
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import time
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from django.core.cache.backends.base import DEFAULT_TIMEOUT, BaseCache
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from django.utils import six
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from django.utils.encoding import force_str
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from django.utils.functional import cached_property
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class BaseMemcachedCache(BaseCache):
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def __init__(self, server, params, library, value_not_found_exception):
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super(BaseMemcachedCache, self).__init__(params)
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if isinstance(server, six.string_types):
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self._servers = server.split(';')
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else:
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self._servers = server
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# The exception type to catch from the underlying library for a key
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# that was not found. This is a ValueError for python-memcache,
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# pylibmc.NotFound for pylibmc, and cmemcache will return None without
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# raising an exception.
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self.LibraryValueNotFoundException = value_not_found_exception
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self._lib = library
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self._options = params.get('OPTIONS')
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@property
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def _cache(self):
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"""
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Implements transparent thread-safe access to a memcached client.
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"""
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if getattr(self, '_client', None) is None:
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self._client = self._lib.Client(self._servers)
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return self._client
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def get_backend_timeout(self, timeout=DEFAULT_TIMEOUT):
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"""
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Memcached deals with long (> 30 days) timeouts in a special
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way. Call this function to obtain a safe value for your timeout.
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"""
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if timeout == DEFAULT_TIMEOUT:
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timeout = self.default_timeout
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if timeout is None:
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# Using 0 in memcache sets a non-expiring timeout.
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return 0
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elif int(timeout) == 0:
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# Other cache backends treat 0 as set-and-expire. To achieve this
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# in memcache backends, a negative timeout must be passed.
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timeout = -1
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if timeout > 2592000: # 60*60*24*30, 30 days
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# See http://code.google.com/p/memcached/wiki/NewProgramming#Expiration
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# "Expiration times can be set from 0, meaning "never expire", to
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# 30 days. Any time higher than 30 days is interpreted as a Unix
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# timestamp date. If you want to expire an object on January 1st of
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# next year, this is how you do that."
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#
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# This means that we have to switch to absolute timestamps.
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timeout += int(time.time())
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return int(timeout)
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def make_key(self, key, version=None):
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# Python 2 memcache requires the key to be a byte string.
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return force_str(super(BaseMemcachedCache, self).make_key(key, version))
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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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return self._cache.add(key, value, self.get_backend_timeout(timeout))
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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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val = self._cache.get(key)
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if val is None:
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return default
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return val
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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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if not self._cache.set(key, value, self.get_backend_timeout(timeout)):
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# make sure the key doesn't keep its old value in case of failure to set (memcached's 1MB limit)
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self._cache.delete(key)
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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._cache.delete(key)
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def get_many(self, keys, version=None):
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new_keys = [self.make_key(x, version=version) for x in keys]
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ret = self._cache.get_multi(new_keys)
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if ret:
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_ = {}
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m = dict(zip(new_keys, keys))
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for k, v in ret.items():
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_[m[k]] = v
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ret = _
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return ret
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def close(self, **kwargs):
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self._cache.disconnect_all()
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def incr(self, key, delta=1, version=None):
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key = self.make_key(key, version=version)
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# memcached doesn't support a negative delta
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if delta < 0:
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return self._cache.decr(key, -delta)
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try:
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val = self._cache.incr(key, delta)
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# python-memcache responds to incr on non-existent keys by
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# raising a ValueError, pylibmc by raising a pylibmc.NotFound
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# and Cmemcache returns None. In all cases,
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# we should raise a ValueError though.
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except self.LibraryValueNotFoundException:
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val = None
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if val is None:
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raise ValueError("Key '%s' not found" % key)
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return val
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def decr(self, key, delta=1, version=None):
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key = self.make_key(key, version=version)
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# memcached doesn't support a negative delta
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if delta < 0:
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return self._cache.incr(key, -delta)
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try:
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val = self._cache.decr(key, delta)
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# python-memcache responds to incr on non-existent keys by
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# raising a ValueError, pylibmc by raising a pylibmc.NotFound
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# and Cmemcache returns None. In all cases,
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# we should raise a ValueError though.
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except self.LibraryValueNotFoundException:
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val = None
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if val is None:
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raise ValueError("Key '%s' not found" % key)
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return val
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def set_many(self, data, timeout=DEFAULT_TIMEOUT, version=None):
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safe_data = {}
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for key, value in data.items():
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key = self.make_key(key, version=version)
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safe_data[key] = value
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self._cache.set_multi(safe_data, self.get_backend_timeout(timeout))
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def delete_many(self, keys, version=None):
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l = lambda x: self.make_key(x, version=version)
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self._cache.delete_multi(map(l, keys))
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def clear(self):
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self._cache.flush_all()
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class MemcachedCache(BaseMemcachedCache):
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"An implementation of a cache binding using python-memcached"
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def __init__(self, server, params):
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import memcache
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super(MemcachedCache, self).__init__(server, params,
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library=memcache,
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value_not_found_exception=ValueError)
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@property
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def _cache(self):
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if getattr(self, '_client', None) is None:
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self._client = self._lib.Client(self._servers, pickleProtocol=pickle.HIGHEST_PROTOCOL)
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return self._client
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class PyLibMCCache(BaseMemcachedCache):
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"An implementation of a cache binding using pylibmc"
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def __init__(self, server, params):
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import pylibmc
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super(PyLibMCCache, self).__init__(server, params,
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library=pylibmc,
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value_not_found_exception=pylibmc.NotFound)
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@cached_property
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def _cache(self):
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client = self._lib.Client(self._servers)
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if self._options:
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client.behaviors = self._options
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return client
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