diff options
| -rw-r--r-- | feeds.py | 28 |
1 files changed, 14 insertions, 14 deletions
@@ -12,6 +12,8 @@ from main.models import Arch, Repo, Package from news.models import News CACHE_TIMEOUT = 1800 +INVALIDATE_TIMEOUT = 15 + CACHE_PACKAGE_KEY = 'cache_package_latest' CACHE_NEWS_KEY = 'cache_news_latest' @@ -36,7 +38,10 @@ def retrieve_package_latest(): latest = Package.objects.values('last_update').latest( 'last_update')['last_update'] latest = latest + utc_offset() - cache.set(CACHE_PACKAGE_KEY, latest, CACHE_TIMEOUT) + # 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_PACKAGE_KEY, latest, CACHE_TIMEOUT) return latest except Package.DoesNotExist: pass @@ -45,11 +50,10 @@ def retrieve_package_latest(): def refresh_package_latest(**kwargs): # 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. Update it instead. - latest = Package.objects.values('last_update').latest( - 'last_update')['last_update'] - latest = latest + utc_offset() - cache.set(CACHE_PACKAGE_KEY, latest, CACHE_TIMEOUT) + # 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) def package_etag(request, *args, **kwargs): latest = retrieve_package_latest() @@ -123,20 +127,16 @@ def retrieve_news_latest(): latest = News.objects.values('last_modified').latest( 'last_modified')['last_modified'] latest = latest + utc_offset() - cache.set(CACHE_NEWS_KEY, latest, CACHE_TIMEOUT) + # same thoughts apply as in retrieve_package_latest + cache.add(CACHE_NEWS_KEY, latest, CACHE_TIMEOUT) return latest except News.DoesNotExist: pass return None def refresh_news_latest(**kwargs): - # 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. Update it instead. - latest = News.objects.values('last_modified').latest( - 'last_modified')['last_modified'] - latest = latest + utc_offset() - cache.set(CACHE_NEWS_KEY, latest, CACHE_TIMEOUT) + # same thoughts apply as in refresh_package_latest + cache.set(CACHE_NEWS_KEY, None, INVALIDATE_TIMEOUT) def news_etag(request, *args, **kwargs): latest = retrieve_news_latest() |