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Add error threshold - better explanation #314

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Add error threshold - better explanation #314

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3c21e98
add error threshold
markddavidoff Nov 8, 2017
a017d98
fix none <> flaot conversion from options
markddavidoff Nov 9, 2017
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63 changes: 61 additions & 2 deletions django_redis/cache.py
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Original file line number Diff line number Diff line change
@@ -1,17 +1,21 @@
import functools
import logging
import time
from threading import RLock

from django.conf import settings
from django.core.cache.backends.base import BaseCache

from .util import load_class
from .exceptions import ConnectionInterrupted

from .util import load_class

DJANGO_REDIS_IGNORE_EXCEPTIONS = getattr(settings, "DJANGO_REDIS_IGNORE_EXCEPTIONS", False)
DJANGO_REDIS_LOG_IGNORED_EXCEPTIONS = getattr(settings, "DJANGO_REDIS_LOG_IGNORED_EXCEPTIONS", False)
DJANGO_REDIS_LOGGER = getattr(settings, "DJANGO_REDIS_LOGGER", False)
DJANGO_REDIS_SCAN_ITERSIZE = getattr(settings, "DJANGO_REDIS_SCAN_ITERSIZE", 10)
DJANGO_REDIS_EXCEPTION_THRESHOLD = getattr(settings, "DJANGO_REDIS_EXCEPTION_THRESHOLD", None)
DJANGO_REDIS_EXCEPTION_THRESHOLD_TIME_WINDOW = getattr(settings, "DJANGO_REDIS_EXCEPTION_TIME_WINDOW", 1)
DJANGO_REDIS_EXCEPTION_THRESHOLD_COOLDOWN = getattr(settings, "DJANGO_REDIS_EXCEPTION_THRESHOLD_COOLDOWN", 5)
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An alternative way might be a "maximum total exception timeout" and a "cooldown time" where you can set 2 times, say '15 seconds', '5 minutes' (respectively) and if the total time spent on timeouts on back to back requests without a success is 15 seconds, silence exceptions for 5 minutes



if DJANGO_REDIS_LOG_IGNORED_EXCEPTIONS:
Expand All @@ -30,8 +34,15 @@ def omit_exception(method=None, return_value=None):
@functools.wraps(method)
def _decorator(self, *args, **kwargs):
try:
if self._exception_threshold and self._exception_threshold_hit():
if DJANGO_REDIS_LOG_IGNORED_EXCEPTIONS:
logger.error("Django Redis exception threshold reached! Skipping cache call.")
return return_value

return method(self, *args, **kwargs)
except ConnectionInterrupted as e:
if self._exception_threshold:
self._incr_exception_counter()
if self._ignore_exceptions:
if DJANGO_REDIS_LOG_IGNORED_EXCEPTIONS:
logger.error(str(e))
Expand All @@ -53,6 +64,54 @@ def __init__(self, server, params):
self._client = None

self._ignore_exceptions = options.get("IGNORE_EXCEPTIONS", DJANGO_REDIS_IGNORE_EXCEPTIONS)
self._exception_threshold = options.get("EXCEPTION_THRESHOLD", DJANGO_REDIS_EXCEPTION_THRESHOLD)
if self._exception_threshold is not None:
self._exception_threshold = float(self._exception_threshold)
self._exception_threshold_cooldown = float(options.get(
"EXCEPTION_THRESHOLD_COOLDOWN", DJANGO_REDIS_EXCEPTION_THRESHOLD_COOLDOWN))
self._exception_threshold_time_window = float(options.get(
"EXCEPTION_THRESHOLD_TIME_WINDOW", DJANGO_REDIS_EXCEPTION_THRESHOLD_TIME_WINDOW))
RedisCache._window_end_time = (time.time() + self._exception_threshold_time_window)

_exception_counter_lock = RLock()
_exception_counter = 0
_exception_threshold_reset_at_time = None
_window_end_time = None

def _incr_exception_counter(self):
now = time.time()
with RedisCache._exception_counter_lock:
if RedisCache._exception_threshold_reset_at_time:
# threshold already hit don't do anything
return

if RedisCache._window_end_time < now:
# if past window, reset everything
RedisCache._exception_counter = 0
RedisCache._window_end_time = (time.time() + self._exception_threshold_time_window)

if RedisCache._exception_counter > self._exception_threshold:
# exceeded threshold
RedisCache._exception_threshold_reset_at_time = (
time.time() + self._exception_threshold_cooldown)
RedisCache._exception_counter = 0
else:
RedisCache._exception_counter += 1

@staticmethod
def _exception_threshold_hit():
now = time.time()

if not RedisCache._exception_threshold_reset_at_time:
return False

if RedisCache._exception_threshold_reset_at_time >= now:
return True

with RedisCache._exception_counter_lock:
# reset threshold
RedisCache._exception_threshold_reset_at_time = None
return False

@property
def client(self):
Expand Down