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OpenStack Study: memcached.py**** CubicPower OpenStack Study ****
# Copyright (c) 2010-2012 OpenStack Foundation # # Licensed under the Apache License, Version 2.0 (the "License"); # you may not use this file except in compliance with the License. # You may obtain a copy of the License at # # http://www.apache.org/licenses/LICENSE-2.0 # # Unless required by applicable law or agreed to in writing, software # distributed under the License is distributed on an "AS IS" BASIS, # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or # implied. # See the License for the specific language governing permissions and # limitations under the License. """ Why our own memcache client? By Michael Barton python-memcached doesn't use consistent hashing, so adding or removing a memcache server from the pool invalidates a huge percentage of cached items. If you keep a pool of python-memcached client objects, each client object has its own connection to every memcached server, only one of which is ever in use. So you wind up with n * m open sockets and almost all of them idle. This client effectively has a pool for each server, so the number of backend connections is hopefully greatly reduced. python-memcache uses pickle to store things, and there was already a huge stink about Swift using pickles in memcache (http://osvdb.org/show/osvdb/86581). That seemed sort of unfair, since nova and keystone and everyone else use pickles for memcache too, but it's hidden behind a "standard" library. But changing would be a security regression at this point. Also, pylibmc wouldn't work for us because it needs to use python sockets in order to play nice with eventlet. Lucid comes with memcached: v1.4.2. Protocol documentation for that version is at: http://github.com/memcached/memcached/blob/1.4.2/doc/protocol.txt """ import cPickle as pickle import logging import time from bisect import bisect from swift import gettext_ as _ from hashlib import md5 from distutils.version import StrictVersion from eventlet.green import socket from eventlet.pools import Pool from eventlet import Timeout, __version__ as eventlet_version from swift.common.utils import json DEFAULT_MEMCACHED_PORT = 11211 CONN_TIMEOUT = 0.3 POOL_TIMEOUT = 1.0 # WAG IO_TIMEOUT = 2.0 PICKLE_FLAG = 1 JSON_FLAG = 2 NODE_WEIGHT = 50 PICKLE_PROTOCOL = 2 TRY_COUNT = 3 # if ERROR_LIMIT_COUNT errors occur in ERROR_LIMIT_TIME seconds, the server # will be considered failed for ERROR_LIMIT_DURATION seconds. ERROR_LIMIT_COUNT = 10 ERROR_LIMIT_TIME = 60 ERROR_LIMIT_DURATION = 60
**** CubicPower OpenStack Study **** def md5hash(key): return md5(key).hexdigest()
**** CubicPower OpenStack Study **** def sanitize_timeout(timeout): """ Sanitize a timeout value to use an absolute expiration time if the delta is greater than 30 days (in seconds). Note that the memcached server translates negative values to mean a delta of 30 days in seconds (and 1 additional second), client beware. """ if timeout > (30 * 24 * 60 * 60): timeout += time.time() return timeout
**** CubicPower OpenStack Study **** class MemcacheConnectionError(Exception): pass
**** CubicPower OpenStack Study **** class MemcachePoolTimeout(Timeout): pass
**** CubicPower OpenStack Study **** class MemcacheConnPool(Pool): """Connection pool for Memcache Connections"""
**** CubicPower OpenStack Study **** def __init__(self, server, size, connect_timeout): Pool.__init__(self, max_size=size) self.server = server self._connect_timeout = connect_timeout self._parent_class_getter = super(MemcacheConnPool, self).get try: # call the patched .get() if eventlet is older than 0.9.17 if StrictVersion(eventlet_version) < StrictVersion('0.9.17'): self._parent_class_getter = self._upstream_fixed_get except ValueError: # "invalid" version number or otherwise error parsing version pass
**** CubicPower OpenStack Study **** def create(self): if ':' in self.server: host, port = self.server.split(':') else: host = self.server port = DEFAULT_MEMCACHED_PORT sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM) sock.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1) with Timeout(self._connect_timeout): sock.connect((host, int(port))) return (sock.makefile(), sock)
**** CubicPower OpenStack Study **** def get(self): fp, sock = self._parent_class_getter() if fp is None: # An error happened previously, so we need a new connection fp, sock = self.create() return fp, sock # The following method is from eventlet post 0.9.16. This version # properly keeps track of pool size accounting, and therefore doesn't # let the pool grow without bound. This patched version is the result # of commit f5e5b2bda7b442f0262ee1084deefcc5a1cc0694 in eventlet and is # documented at https://bitbucket.org/eventlet/eventlet/issue/91
**** CubicPower OpenStack Study **** def _upstream_fixed_get(self): """Return an item from the pool, when one is available. This may cause the calling greenthread to block. """ if self.free_items: return self.free_items.popleft() self.current_size += 1 if self.current_size <= self.max_size: try: created = self.create() except: # noqa self.current_size -= 1 raise return created self.current_size -= 1 # did not create return self.channel.get()
**** CubicPower OpenStack Study **** class MemcacheRing(object): """ Simple, consistent-hashed memcache client. """
**** CubicPower OpenStack Study **** def __init__(self, servers, connect_timeout=CONN_TIMEOUT, io_timeout=IO_TIMEOUT, pool_timeout=POOL_TIMEOUT, tries=TRY_COUNT, allow_pickle=False, allow_unpickle=False, max_conns=2): self._ring = {} self._errors = dict(((serv, []) for serv in servers)) self._error_limited = dict(((serv, 0) for serv in servers)) for server in sorted(servers): for i in xrange(NODE_WEIGHT): self._ring[md5hash('%s-%s' % (server, i))] = server self._tries = tries if tries <= len(servers) else len(servers) self._sorted = sorted(self._ring) self._client_cache = dict(((server, MemcacheConnPool(server, max_conns, connect_timeout)) for server in servers)) self._connect_timeout = connect_timeout self._io_timeout = io_timeout self._pool_timeout = pool_timeout self._allow_pickle = allow_pickle self._allow_unpickle = allow_unpickle or allow_pickle
**** CubicPower OpenStack Study **** def _exception_occurred(self, server, e, action='talking', sock=None, fp=None, got_connection=True): if isinstance(e, Timeout): logging.error(_("Timeout %(action)s to memcached: %(server)s"), {'action': action, 'server': server}) else: logging.exception(_("Error %(action)s to memcached: %(server)s"), {'action': action, 'server': server}) try: if fp: fp.close() del fp except Exception: pass try: if sock: sock.close() del sock except Exception: pass if got_connection: # We need to return something to the pool # A new connection will be created the next time it is retreived self._return_conn(server, None, None) now = time.time() self._errors[server].append(time.time()) if len(self._errors[server]) > ERROR_LIMIT_COUNT: self._errors[server] = [err for err in self._errors[server] if err > now - ERROR_LIMIT_TIME] if len(self._errors[server]) > ERROR_LIMIT_COUNT: self._error_limited[server] = now + ERROR_LIMIT_DURATION logging.error(_('Error limiting server %s'), server)
**** CubicPower OpenStack Study **** def _get_conns(self, key): """ Retrieves a server conn from the pool, or connects a new one. Chooses the server based on a consistent hash of "key". """ pos = bisect(self._sorted, key) served = [] while len(served) < self._tries: pos = (pos + 1) % len(self._sorted) server = self._ring[self._sorted[pos]] if server in served: continue served.append(server) if self._error_limited[server] > time.time(): continue sock = None try: with MemcachePoolTimeout(self._pool_timeout): fp, sock = self._client_cache[server].get() yield server, fp, sock except MemcachePoolTimeout as e: self._exception_occurred( server, e, action='getting a connection', got_connection=False) except (Exception, Timeout) as e: # Typically a Timeout exception caught here is the one raised # by the create() method of this server's MemcacheConnPool # object. self._exception_occurred( server, e, action='connecting', sock=sock)
**** CubicPower OpenStack Study **** def _return_conn(self, server, fp, sock): """Returns a server connection to the pool.""" self._client_cache[server].put((fp, sock))
**** CubicPower OpenStack Study **** def set(self, key, value, serialize=True, timeout=0, time=0, min_compress_len=0): """ Set a key/value pair in memcache :param key: key :param value: value :param serialize: if True, value is serialized with JSON before sending to memcache, or with pickle if configured to use pickle instead of JSON (to avoid cache poisoning) :param timeout: ttl in memcache, this parameter is now deprecated. It will be removed in next release of OpenStack, use time parameter instead in the future :time: equivalent to timeout, this parameter is added to keep the signature compatible with python-memcached interface. This implementation will take this value and sign it to the parameter timeout :min_compress_len: minimum compress length, this parameter was added to keep the signature compatible with python-memcached interface. This implementation ignores it. """ key = md5hash(key) if timeout: logging.warn("parameter timeout has been deprecated, use time") timeout = sanitize_timeout(time or timeout) flags = 0 if serialize and self._allow_pickle: value = pickle.dumps(value, PICKLE_PROTOCOL) flags |= PICKLE_FLAG elif serialize: value = json.dumps(value) flags |= JSON_FLAG for (server, fp, sock) in self._get_conns(key): try: with Timeout(self._io_timeout): sock.sendall('set %s %d %d %s\r\n%s\r\n' % (key, flags, timeout, len(value), value)) # Wait for the set to complete fp.readline() self._return_conn(server, fp, sock) return except (Exception, Timeout) as e: self._exception_occurred(server, e, sock=sock, fp=fp)
**** CubicPower OpenStack Study **** def get(self, key): """ Gets the object specified by key. It will also unserialize the object before returning if it is serialized in memcache with JSON, or if it is pickled and unpickling is allowed. :param key: key :returns: value of the key in memcache """ key = md5hash(key) value = None for (server, fp, sock) in self._get_conns(key): try: with Timeout(self._io_timeout): sock.sendall('get %s\r\n' % key) line = fp.readline().strip().split() while line[0].upper() != 'END': if line[0].upper() == 'VALUE' and line[1] == key: size = int(line[3]) value = fp.read(size) if int(line[2]) & PICKLE_FLAG: if self._allow_unpickle: value = pickle.loads(value) else: value = None elif int(line[2]) & JSON_FLAG: value = json.loads(value) fp.readline() line = fp.readline().strip().split() self._return_conn(server, fp, sock) return value except (Exception, Timeout) as e: self._exception_occurred(server, e, sock=sock, fp=fp)
**** CubicPower OpenStack Study **** def incr(self, key, delta=1, time=0, timeout=0): """ Increments a key which has a numeric value by delta. If the key can't be found, it's added as delta or 0 if delta < 0. If passed a negative number, will use memcached's decr. Returns the int stored in memcached Note: The data memcached stores as the result of incr/decr is an unsigned int. decr's that result in a number below 0 are stored as 0. :param key: key :param delta: amount to add to the value of key (or set as the value if the key is not found) will be cast to an int :param time: the time to live. This parameter deprecates parameter timeout. The addition of this parameter is to make the interface consistent with set and set_multi methods :param timeout: ttl in memcache, deprecated, will be removed in future OpenStack releases :returns: result of incrementing :raises MemcacheConnectionError: """ if timeout: logging.warn("parameter timeout has been deprecated, use time") key = md5hash(key) command = 'incr' if delta < 0: command = 'decr' delta = str(abs(int(delta))) timeout = sanitize_timeout(time or timeout) for (server, fp, sock) in self._get_conns(key): try: with Timeout(self._io_timeout): sock.sendall('%s %s %s\r\n' % (command, key, delta)) line = fp.readline().strip().split() if line[0].upper() == 'NOT_FOUND': add_val = delta if command == 'decr': add_val = '0' sock.sendall('add %s %d %d %s\r\n%s\r\n' % (key, 0, timeout, len(add_val), add_val)) line = fp.readline().strip().split() if line[0].upper() == 'NOT_STORED': sock.sendall('%s %s %s\r\n' % (command, key, delta)) line = fp.readline().strip().split() ret = int(line[0].strip()) else: ret = int(add_val) else: ret = int(line[0].strip()) self._return_conn(server, fp, sock) return ret except (Exception, Timeout) as e: self._exception_occurred(server, e, sock=sock, fp=fp) raise MemcacheConnectionError("No Memcached connections succeeded.")
**** CubicPower OpenStack Study **** def decr(self, key, delta=1, time=0, timeout=0): """ Decrements a key which has a numeric value by delta. Calls incr with -delta. :param key: key :param delta: amount to subtract to the value of key (or set the value to 0 if the key is not found) will be cast to an int :param time: the time to live. This parameter depcates parameter timeout. The addition of this parameter is to make the interface consistent with set and set_multi methods :param timeout: ttl in memcache, deprecated, will be removed in future OpenStack releases :returns: result of decrementing :raises MemcacheConnectionError: """ if timeout: logging.warn("parameter timeout has been deprecated, use time") return self.incr(key, delta=-delta, time=(time or timeout))
**** CubicPower OpenStack Study **** def delete(self, key): """ Deletes a key/value pair from memcache. :param key: key to be deleted """ key = md5hash(key) for (server, fp, sock) in self._get_conns(key): try: with Timeout(self._io_timeout): sock.sendall('delete %s\r\n' % key) # Wait for the delete to complete fp.readline() self._return_conn(server, fp, sock) return except (Exception, Timeout) as e: self._exception_occurred(server, e, sock=sock, fp=fp)
**** CubicPower OpenStack Study **** def set_multi(self, mapping, server_key, serialize=True, timeout=0, time=0, min_compress_len=0): """ Sets multiple key/value pairs in memcache. :param mapping: dictonary of keys and values to be set in memcache :param servery_key: key to use in determining which server in the ring is used :param serialize: if True, value is serialized with JSON before sending to memcache, or with pickle if configured to use pickle instead of JSON (to avoid cache poisoning) :param timeout: ttl for memcache. This parameter is now deprecated, it will be removed in next release of OpenStack, use time parameter instead in the future :time: equalvent to timeout, this parameter is added to keep the signature compatible with python-memcached interface. This implementation will take this value and sign it to parameter timeout :min_compress_len: minimum compress length, this parameter was added to keep the signature compatible with python-memcached interface. This implementation ignores it """ if timeout: logging.warn("parameter timeout has been deprecated, use time") server_key = md5hash(server_key) timeout = sanitize_timeout(time or timeout) msg = '' for key, value in mapping.iteritems(): key = md5hash(key) flags = 0 if serialize and self._allow_pickle: value = pickle.dumps(value, PICKLE_PROTOCOL) flags |= PICKLE_FLAG elif serialize: value = json.dumps(value) flags |= JSON_FLAG msg += ('set %s %d %d %s\r\n%s\r\n' % (key, flags, timeout, len(value), value)) for (server, fp, sock) in self._get_conns(server_key): try: with Timeout(self._io_timeout): sock.sendall(msg) # Wait for the set to complete for _ in range(len(mapping)): fp.readline() self._return_conn(server, fp, sock) return except (Exception, Timeout) as e: self._exception_occurred(server, e, sock=sock, fp=fp)
**** CubicPower OpenStack Study **** def get_multi(self, keys, server_key): """ Gets multiple values from memcache for the given keys. :param keys: keys for values to be retrieved from memcache :param servery_key: key to use in determining which server in the ring is used :returns: list of values """ server_key = md5hash(server_key) keys = [md5hash(key) for key in keys] for (server, fp, sock) in self._get_conns(server_key): try: with Timeout(self._io_timeout): sock.sendall('get %s\r\n' % ' '.join(keys)) line = fp.readline().strip().split() responses = {} while line[0].upper() != 'END': if line[0].upper() == 'VALUE': size = int(line[3]) value = fp.read(size) if int(line[2]) & PICKLE_FLAG: if self._allow_unpickle: value = pickle.loads(value) else: value = None elif int(line[2]) & JSON_FLAG: value = json.loads(value) responses[line[1]] = value fp.readline() line = fp.readline().strip().split() values = [] for key in keys: if key in responses: values.append(responses[key]) else: values.append(None) self._return_conn(server, fp, sock) return values except (Exception, Timeout) as e: self._exception_occurred(server, e, sock=sock, fp=fp)
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