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"""
Developed by niphlod@gmail.com
Released under web2py license because includes gluon/cache.py source code
"""
try:
import cPickle as pickle
except:
import pickle
import time
import re
import logging
import thread
import random
from gluon import current
from gluon.cache import CacheAbstract
from gluon.contrib.redis_utils import acquire_lock, release_lock
from gluon.contrib.redis_utils import register_release_lock, RConnectionError
logger = logging.getLogger("web2py.cache.redis")
locker = thread.allocate_lock()
def RedisCache(redis_conn=None, debug=False, with_lock=False, fail_gracefully=False, db=None):
"""
Usage example: put in models::
First of all install Redis
Ubuntu :
sudo apt-get install redis-server
sudo pip install redis
Then
from gluon.contrib.redis_utils import RConn
rconn = RConn()
from gluon.contrib.redis_cache import RedisCache
cache.redis = RedisCache(redis_conn=rconn, debug=True, with_lock=True)
Args:
redis_conn: a redis-like connection object
debug: if True adds to stats() the total_hits and misses
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
fail_gracefully: if redis is unavailable, returns the value computing it
instead of raising an exception
It can be used pretty much the same as cache.ram()
When you use cache.redis directly you can use :
redis_key_and_var_name = cache.redis('redis_key_and_var_name', lambda or function,
time_expire=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:
instance_name = 'redis_instance_' + current.request.application
if not hasattr(RedisCache, instance_name):
setattr(RedisCache, instance_name,
RedisClient(redis_conn=redis_conn, debug=debug,
with_lock=with_lock, fail_gracefully=fail_gracefully))
return getattr(RedisCache, instance_name)
finally:
locker.release()
class RedisClient(object):
meta_storage = {}
MAX_RETRIES = 5
RETRIES = 0
def __init__(self, redis_conn=None, debug=False,
with_lock=False, fail_gracefully=False):
self.request = current.request
self.debug = debug
self.with_lock = with_lock
self.fail_gracefully = fail_gracefully
self.prefix = "w2p:cache:%s:" % self.request.application
if self.request:
app = self.request.application
else:
app = ''
if app not 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_conn
self._release_script = register_release_lock(self.r_server)
def initialize(self):
pass
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:
if f is None:
# delete and never look back
self.r_server.delete(newKey)
return None
# 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)
else:
# naive distributed locking
if with_lock:
lock_key = '%s:__lock' % newKey
randomvalue = time.time()
al = acquire_lock(self.r_server, lock_key, randomvalue)
# someone may have computed it
obj = self.r_server.get(newKey)
if obj is None:
value = self.cache_it(newKey, f, time_expire)
else:
value = pickle.loads(obj)
release_lock(self, lock_key, al)
else:
# without distributed locking
value = self.cache_it(newKey, f, time_expire)
return value
except RConnectionError:
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
expire_at = int(time.time() + time_expire) + 120
bucket_key = "%s:%s" % (cache_set_key, expire_at / 60)
value = f()
value_ = pickle.dumps(value, pickle.HIGHEST_PROTOCOL)
if time_expire == 0:
time_expire = 1
self.r_server.setex(key, time_expire, value_)
# print '%s will expire on %s: it goes in bucket %s' % (key, time.ctime(expire_at))
# print 'that will expire on %s' % (bucket_key, time.ctime(((expire_at / 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, time_expire, value_)
# add the key to the bucket
p.sadd(bucket_key, key)
# expire the bucket properly
p.expireat(bucket_key, ((expire_at / 60) + 1) * 60)
p.execute()
return value
def retry_call(self, key, f, time_expire, with_lock):
self.RETRIES += 1
if self.RETRIES <= self.MAX_RETRIES:
logger.error("sleeping %s seconds before reconnecting" % (2 * self.RETRIES))
time.sleep(2 * self.RETRIES)
if self.fail_gracefully:
self.RETRIES = 0
return f()
return self.__call__(key, f, time_expire, with_lock)
else:
self.RETRIES = 0
if self.fail_gracefully:
return f
raise RConnectionError('Redis instance is unavailable')
def increment(self, key, value=1):
try:
newKey = self.__keyFormat__(key)
return self.r_server.incr(newKey, value)
except RConnectionError:
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)
return self.increment(key, value)
else:
self.RETRIES = 0
raise RConnectionError('Redis instance is unavailable')
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):
stats_collector = self.r_server.info()
if self.debug:
stats_collector['w2p_stats'] = dict(
hit_total=self.r_server.get(
'web2py_cache_statistics:hit_total'),
misses=self.r_server.get('web2py_cache_statistics:misses')
)
stats_collector['w2p_keys'] = dict()
for a in self.r_server.keys("w2p:%s:*" % (
self.request.application)):
stats_collector['w2p_keys']["%s_expire_in_sec" % a] = self.r_server.ttl(a)
return stats_collector
def __keyFormat__(self, key):
return '%s%s' % (self.prefix, key.replace(' ', '_'))
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