""" Developed by niphlod@gmail.com Released under web2py license because includes gluon/cache.py source code """ import redis from redis.exceptions import ConnectionError from gluon import current from gluon.cache import CacheAbstract import cPickle as pickle import time import re import logging import thread import random logger = logging.getLogger("web2py.cache.redis") locker = thread.allocate_lock() def RedisCache(*args, **vars): """ Usage example: put in models from gluon.contrib.redis_cache import RedisCache cache.redis = RedisCache('localhost:6379',db=None, debug=True, with_lock=True) :param db: redis db to use (0..16) :param debug: if True adds to stats() the total_hits and misses :param with_lock: sets the default locking mode for creating new keys. By default is False (usualy when you choose Redis you do it for performances reason) When True, only one thread/process can set a value concurrently When you use cache.redis directly you can use value = cache.redis('mykey', lambda: time.time(), with_lock=True) to enforce locking. The with_lock parameter overrides the one set in the cache.redis instance creation cache.redis.stats() returns a dictionary with statistics of Redis server with one additional key ('w2p_keys') showing all keys currently set from web2py with their TTL A little wording on how keys are stored (and why the cache_it() function and the clear() one look a little bit convoluted): there are a lot of libraries that just store values and then use the KEYS command to delete it. Until recent releases of this module, that technique was used here too. In the need of deleting specific keys in a database with zillions keys in it (other web2py apps, other applications in the need of a Redis stack) the KEYS command is slow (it needs to scan every key in the database). So, we use Redis 'sets' to store keys in "buckets"... - every key created gets "indexed" in a bucket - all buckets are indexed in a fixed key that never expires - all keys generated within the same minute go in the same bucket - every bucket is then set to expire when every key within it is expired When we need to clear() cached keys: - we tell Redis to SUNION all buckets - gives us just the keys that are not expired yet - buckets that are expired are removed from the fixed set - we scan the keys and then delete them """ locker.acquire() try: if not hasattr(RedisCache, 'redis_instance'): RedisCache.redis_instance = RedisClient(*args, **vars) finally: locker.release() return RedisCache.redis_instance class RedisClient(object): meta_storage = {} MAX_RETRIES = 5 RETRIES = 0 def __init__(self, server='localhost:6379', db=None, debug=False, with_lock=False): self.server = server self.db = db or 0 host, port = (self.server.split(':') + ['6379'])[:2] port = int(port) self.request = current.request self.debug = debug self.with_lock = with_lock self.prefix = "w2p:%s:" % (self.request.application) if self.request: app = self.request.application else: app = '' if not app in self.meta_storage: self.storage = self.meta_storage[app] = { CacheAbstract.cache_stats_name: { 'hit_total': 0, 'misses': 0, }} else: self.storage = self.meta_storage[app] self.cache_set_key = 'w2p:%s:___cache_set' % (self.request.application) self.r_server = redis.Redis(host=host, port=port, db=self.db) def __call__(self, key, f, time_expire=300, with_lock=None): if with_lock is None: with_lock = self.with_lock if time_expire is None: time_expire = 24 * 60 * 60 newKey = self.__keyFormat__(key) value = None ttl = 0 try: #is there a value obj = self.r_server.get(newKey) #what's its ttl if obj: ttl = self.r_server.ttl(newKey) if ttl > time_expire: obj = None if obj: #was cached if self.debug: self.r_server.incr('web2py_cache_statistics:hit_total') value = pickle.loads(obj) elif f is None: #delete and never look back self.r_server.delete(newKey) else: #naive distributed locking if with_lock: lock_key = '%s:__lock' % newKey try: while True: lock = self.r_server.setnx(lock_key, 1) if lock: value = self.cache_it(newKey, f, time_expire) break else: time.sleep(0.2) #did someone else create it in the meanwhile ? obj = self.r_server.get(newKey) if obj: value = pickle.loads(obj) break finally: self.r_server.delete(lock_key) else: #without distributed locking value = self.cache_it(newKey, f, time_expire) return value except ConnectionError: return self.retry_call(key, f, time_expire, with_lock) def cache_it(self, key, f, time_expire): if self.debug: self.r_server.incr('web2py_cache_statistics:misses') cache_set_key = self.cache_set_key expireat = int(time.time() + time_expire) + 120 bucket_key = "%s:%s" % (cache_set_key, expireat / 60) value = f() value_ = pickle.dumps(value) if time_expire == 0: time_expire = 1 self.r_server.setex(key, value_, time_expire) #print '%s will expire on %s: it goes in bucket %s' % (key, time.ctime(expireat)) #print 'that will expire on %s' % (bucket_key, time.ctime(((expireat/60) + 1)*60)) p = self.r_server.pipeline() #add bucket to the fixed set p.sadd(cache_set_key, bucket_key) #sets the key p.setex(key, value_, time_expire) #add the key to the bucket p.sadd(bucket_key, key) #expire the bucket properly p.expireat(bucket_key, ((expireat/60) + 1)*60) p.execute() return value def retry_call(self, key, f, time_expire, with_locking): self.RETRIES += 1 if self.RETRIES <= self.MAX_RETRIES: logger.error("sleeping %s seconds before reconnecting" % (2 * self.RETRIES)) time.sleep(2 * self.RETRIES) self.__init__(self.server, self.db, self.debug, self.with_lock) return self.__call__(key, f, time_expire, with_locking) else: self.RETRIES = 0 raise ConnectionError('Redis instance is unavailable at %s' % ( self.server)) def increment(self, key, value=1): try: newKey = self.__keyFormat__(key) return self.r_server.incr(newKey, value) except ConnectionError: return self.retry_increment(key, value) def retry_increment(self, key, value): self.RETRIES += 1 if self.RETRIES <= self.MAX_RETRIES: logger.error("sleeping some seconds before reconnecting") time.sleep(2 * self.RETRIES) self.__init__(self.server, self.db, self.debug, self.with_lock) return self.increment(key, value) else: self.RETRIES = 0 raise ConnectionError('Redis instance is unavailable at %s' % ( self.server)) def clear(self, regex): """ Auxiliary function called by `clear` to search and clear cache entries """ r = re.compile(regex) #get all buckets buckets = self.r_server.smembers(self.cache_set_key) #get all keys in buckets if buckets: keys = self.r_server.sunion(buckets) else: return prefix = self.prefix pipe = self.r_server.pipeline() for a in keys: if r.match(str(a).replace(prefix, '', 1)): pipe.delete(a) if random.randrange(0,100) < 10: #do this just once in a while (10% chance) self.clear_buckets(buckets) pipe.execute() def clear_buckets(self, buckets): p = self.r_server.pipeline() for b in buckets: if not self.r_server.exists(b): p.srem(self.cache_set_key, b) p.execute() def delete(self, key): newKey = self.__keyFormat__(key) return self.r_server.delete(newKey) def stats(self): statscollector = self.r_server.info() if self.debug: statscollector['w2p_stats'] = dict( hit_total=self.r_server.get( 'web2py_cache_statistics:hit_total'), misses=self.r_server.get('web2py_cache_statistics:misses') ) statscollector['w2p_keys'] = dict() for a in self.r_server.keys("w2p:%s:*" % ( self.request.application)): statscollector['w2p_keys']["%s_expire_in_sec" % (a)] = self.r_server.ttl(a) return statscollector def __keyFormat__(self, key): return '%s%s' % (self.prefix, key.replace(' ', '_'))