194 lines
7.4 KiB
Python
194 lines
7.4 KiB
Python
"Memcached cache backend"
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import pickle
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import re
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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.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().__init__(params)
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if isinstance(server, str):
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self._servers = re.split('[;,]', server)
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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') or {}
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@property
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def _cache(self):
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"""
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Implement 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, **self._options)
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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 https://github.com/memcached/memcached/wiki/Programming#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 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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return self._cache.get(key, default)
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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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key_map = {self.make_key(key, version=version): key for key in keys}
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ret = self._cache.get_multi(key_map.keys())
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return {key_map[k]: v for k, v in ret.items()}
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def close(self, **kwargs):
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# Many clients don't clean up connections properly.
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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 nonexistent 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 nonexistent 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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original_keys = {}
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for key, value in data.items():
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safe_key = self.make_key(key, version=version)
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safe_data[safe_key] = value
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original_keys[safe_key] = key
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failed_keys = self._cache.set_multi(safe_data, self.get_backend_timeout(timeout))
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return [original_keys[k] for k in failed_keys]
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def delete_many(self, keys, version=None):
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self._cache.delete_multi(self.make_key(key, version=version) for key in 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().__init__(server, params, library=memcache, 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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client_kwargs = {'pickleProtocol': pickle.HIGHEST_PROTOCOL}
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client_kwargs.update(self._options)
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self._client = self._lib.Client(self._servers, **client_kwargs)
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return self._client
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def touch(self, key, timeout=DEFAULT_TIMEOUT, version=None):
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key = self.make_key(key, version=version)
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return self._cache.touch(key, self.get_backend_timeout(timeout)) != 0
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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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# python-memcached doesn't support default values in get().
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# https://github.com/linsomniac/python-memcached/issues/159
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# Remove this method if that issue is fixed.
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if val is None:
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return default
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return val
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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().__init__(server, params, library=pylibmc, value_not_found_exception=pylibmc.NotFound)
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@cached_property
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def _cache(self):
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return self._lib.Client(self._servers, **self._options)
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def touch(self, key, timeout=DEFAULT_TIMEOUT, version=None):
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key = self.make_key(key, version=version)
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if timeout == 0:
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return self._cache.delete(key)
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return self._cache.touch(key, self.get_backend_timeout(timeout))
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def close(self, **kwargs):
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# libmemcached manages its own connections. Don't call disconnect_all()
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# as it resets the failover state and creates unnecessary reconnects.
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pass
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