In a django project I only need to cache a few queries, using, because of server limitations, a cache table instead of memcached.

One of those queries looks like this:

Let's say I have a Parent object, which has a lot of Child objects. I need to store the result of the simple query parent.childs.all().

I have no problem with that, and everything works as expected with some code like

key = "%s_children" %(parent.name)
value = cache.get(key)
if value is None:
  cache.set(key, parent.children.all(), CACHE_TIMEOUT)
  value = cache.get(key)

But sometimes, just sometimes, the cache.set does nothing, and, after executing cache.set, cache.get(key) keeps returning None.

After some test, I've noticed that cache.set is not working when parent.children.all().count() has higher values.
That means that if I'm storing inside of key (for example) 600 children objects, it works fine,
but it wont work with 1200 children.

So my question is: is there a limit to the data that a key could store? How can I override it?

key = "%s_children" %(parent.name)
value = cache.get(key)
if value is None:
  value = parent.children.all()
  cache.set(key, value, CACHE_TIMEOUT)

The second version won't cause errors if cache.set doesn't work, so it could be a workaround to my issue, but obviously not a solution.

In general, let's forget about my issue, which version would you consider "better"?