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-rw-r--r--main/utils.py34
1 files changed, 25 insertions, 9 deletions
diff --git a/main/utils.py b/main/utils.py
index d7681cb6..12d12503 100644
--- a/main/utils.py
+++ b/main/utils.py
@@ -6,10 +6,8 @@ from django.core.cache import cache
from django.utils.hashcompat import md5_constructor
CACHE_TIMEOUT = 1800
-INVALIDATE_TIMEOUT = 15
-
-CACHE_PACKAGE_KEY = 'cache_package_latest'
-CACHE_NEWS_KEY = 'cache_news_latest'
+INVALIDATE_TIMEOUT = 10
+CACHE_LATEST_PREFIX = 'cache_latest_'
def cache_function_key(func, args, kwargs):
raw = [func.__name__, func.__module__, args, kwargs]
@@ -53,16 +51,34 @@ make_choice = lambda l: [(str(m), str(m)) for m in l]
# and hoops otherwise. The only thing currently using these keys is the feed
# caching stuff.
-def refresh_package_latest(**kwargs):
+def refresh_latest(**kwargs):
+ '''A post_save signal handler to clear out the cached latest value for a
+ given model.'''
+ cache_key = CACHE_LATEST_PREFIX + kwargs['sender'].__name__
# We could delete the value, but that could open a race condition
# where the new data wouldn't have been committed yet by the calling
# thread. Instead, explicitly set it to None for a short amount of time.
# Hopefully by the time it expires we will have committed, and the cache
# will be valid again. See "Scaling Django" by Mike Malone, slide 30.
- cache.set(CACHE_PACKAGE_KEY, None, INVALIDATE_TIMEOUT)
+ cache.set(cache_key, None, INVALIDATE_TIMEOUT)
-def refresh_news_latest(**kwargs):
- # same thoughts apply as in refresh_package_latest
- cache.set(CACHE_NEWS_KEY, None, INVALIDATE_TIMEOUT)
+def retrieve_latest(sender):
+ # we could break this down based on the request url, but it would probably
+ # cost us more in query time to do so.
+ cache_key = CACHE_LATEST_PREFIX + sender.__name__
+ latest = cache.get(cache_key)
+ if latest:
+ return latest
+ try:
+ latest_by = sender._meta.get_latest_by
+ latest = sender.objects.values(latest_by).latest()[latest_by]
+ # Using add means "don't overwrite anything in there". What could be in
+ # there is an explicit None value that our refresh signal set, which
+ # means we want to avoid race condition possibilities for a bit.
+ cache.add(cache_key, latest, CACHE_TIMEOUT)
+ return latest
+ except sender.DoesNotExist:
+ pass
+ return None
# vim: set ts=4 sw=4 et: