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authorDan McGee <dan@archlinux.org>2011-04-07 16:52:52 -0500
committerDan McGee <dan@archlinux.org>2011-04-07 17:03:13 -0500
commit77842a6c76095277b024505708bf528d455b9c89 (patch)
tree686158efd744d0b35722df92cf91fa55a647e3e8 /main
parentd7665959652171b93db5e084c6738e8e1773e7f0 (diff)
Consolidate caching black magic
Get the stuff used to retrieve and refresh the latest date values all in the same place, and make it a bit more beautiful by refactoring it all into a common set of methods. Signed-off-by: Dan McGee <dan@archlinux.org>
Diffstat (limited to 'main')
-rw-r--r--main/models.py7
-rw-r--r--main/utils.py34
2 files changed, 28 insertions, 13 deletions
diff --git a/main/models.py b/main/models.py
index 8d34731f..38120134 100644
--- a/main/models.py
+++ b/main/models.py
@@ -128,8 +128,7 @@ class Package(models.Model):
class Meta:
db_table = 'packages'
ordering = ('pkgname',)
- #get_latest_by = 'last_update'
- #ordering = ('-last_update',)
+ get_latest_by = 'last_update'
def __unicode__(self):
return self.pkgname
@@ -390,10 +389,10 @@ def set_todolist_fields(sender, **kwargs):
todolist.date_added = datetime.utcnow()
# connect signals needed to keep cache in line with reality
-from main.utils import refresh_package_latest
+from main.utils import refresh_latest
from django.db.models.signals import pre_save, post_save
-post_save.connect(refresh_package_latest, sender=Package,
+post_save.connect(refresh_latest, sender=Package,
dispatch_uid="main.models")
pre_save.connect(set_todolist_fields, sender=Todolist,
dispatch_uid="main.models")
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: