new and improved redis_cache. Got distributed locking and faster clear() function.

also, the .increment() was a little bit bugged.

gluon/contrib/redis_cache.py

@@ -1,8 +1,7 @@
 """
-Developed by 616d41631bff906704951934ffe4015e
+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
@@ -12,6 +11,8 @@ import time
 import re
 import logging
 import thread
+import random
+
 
 logger = logging.getLogger("web2py.cache.redis")
 
@@ -23,15 +24,42 @@ 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)
+    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
-    return a dictionary with statistics of Redis server
         with one additional key ('w2p_keys') showing all keys currently set
         from web2py with their TTL
-    if debug=True additional tracking is activate and another key is added
+
-    ('w2p_stats') showing total_hits and misses
+    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()
@@ -49,13 +77,15 @@ class RedisClient(object):
     MAX_RETRIES = 5
     RETRIES = 0
 
-    def __init__(self, server='localhost:6379', db=None, debug=False):
+    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:
@@ -70,67 +100,112 @@ class RedisClient(object):
         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):
+    def __call__(self, key, f, time_expire=300, with_lock=None):
-        try:
+        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)
-            ttl = self.r_server.ttl(newKey) or 0
+            #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:
-                if self.debug:
+                #naive distributed locking
-                    self.r_server.incr('web2py_cache_statistics:misses')
+                if with_lock:
-                value = f()
+                    lock_key = '%s:__lock' % newKey
-                if time_expire == 0:
+                    try:
-                    time_expire = 1
+                        while True:
-                self.r_server.setex(newKey, pickle.dumps(value), time_expire)
+                            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)
+            return self.retry_call(key, f, time_expire, with_lock)
 
-    def retry_call(self, key, f, time_expire):
+    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.__init__(self.server, self.db, self.debug, self.with_lock)
-            return self.__call__(key, f, time_expire)
+            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, time_expire=300):
+    def increment(self, key, value=1):
         try:
             newKey = self.__keyFormat__(key)
-            obj = self.r_server.get(newKey)
-            if obj:
             return self.r_server.incr(newKey, value)
-            else:
-                self.r_server.setex(newKey, value, time_expire)
-                return value
         except ConnectionError:
-            return self.retry_increment(key, value, time_expire)
+            return self.retry_increment(key, value)
 
-    def retry_increment(self, key, value, time_expire):
+    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.__init__(self.server, self.db, self.debug, self.with_lock)
-            return self.increment(key, value, time_expire)
+            return self.increment(key, value)
         else:
             self.RETRIES = 0
             raise ConnectionError('Redis instance is unavailable at %s' % (
@@ -142,14 +217,34 @@ class RedisClient(object):
         clear cache entries
         """
         r = re.compile(regex)
-        prefix = "w2p:%s:" % (self.request.application)
+        #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 self.r_server.keys("%s*" %
+        for a in keys:
-                                    (prefix)):
             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:
@@ -159,12 +254,11 @@ class RedisClient(object):
                 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)] = \
+            statscollector['w2p_keys']["%s_expire_in_sec" % (a)] = self.r_server.ttl(a)
-                self.r_server.ttl(a)
         return statscollector
 
     def __keyFormat__(self, key):
-        return 'w2p:%s:%s' % (self.request.application,
+        return '%s%s' % (self.prefix, key.replace(' ', '_'))
-                              key.replace(' ', '_'))