You're right: there are no guarantees around how long an item will stay in
Memcache. Memcache has two Least-Recently-Used lists of items, where if you
don't read or write an item, it may be pushed off the list for space.
There's a per app LRU and a global LRU for apps sharing the same memcache
My objects remain in the memcache only for about 5 minutes. I know that
there is no guarantee about the caching period, but this seems abnormal.
I've read that lack of memory could be the reason. The size of one object is
about 50K, and I typically cache less as 50 objects.
I have no flush
