the paragraph "When_to_Use_a_Memory_Cache" of the docu explains it
well:
http://bit.ly/3LMsR9

On Oct 30, 11:11 pm, loell <[email protected]> wrote:
> sorry to get back at this discussion so late,  but i have another
> question in relation to this behavior / operation,  so how would one
> effectively design a correct memcaching of data from the data store?
> is it just,
>
> evaluate all items in the memcache set, and if there is no "none" then
> OK.
> else repeat the GQL operation then reset all memcache items again in
> the memcache set.
>
> is this the only way?
>
> On Oct 28, 6:07 pm, "Nick Johnson (Google)" <[email protected]>
> wrote:
>
> > Hi loell,
>
> > Memcache is, as the name implies, a cache. Any key may be evicted at any
> > time, though frequently read keys will be evicted less often. You should not
> > design your app to rely on the persistence of memcache entries.
>
> > -Nick Johnson
>
> > On Tue, Oct 27, 2009 at 11:02 PM, loell <[email protected]> wrote:
>
> > > Currently I only cache roughly 349 items with the total size of only
> > > 2.9 KB.  which is more puzzling as it's just a single dot in the total
> > > memcache size quota of 10 MB :(
>
> > > I'm beginning to think that maybe this particular web app is sitting
> > > on an unstable part of the cloud?  I even don't have a cron Job or a
> > > task queue yet, that might affect memcache items.
>
> > > On Oct 28, 2:19 am, Wooble <[email protected]> wrote:
> > > > How much are you caching?  Items are removed from the cache when
> > > > you're storing too much (I don't believe there's a published limit,
> > > > but I've seen anecdotal claims of 10MB), with the least recently used
> > > > items evicted first.
>
> > > > On Oct 27, 1:56 pm, loell <[email protected]> wrote:
>
> > > > > additional info: the Items in question are still retrievable in just a
> > > > > couple of minutes, usually.  but after that,  it just returns none.
> > > > > while part of the items in that set is still retrievable and all other
> > > > > memcache sets are still intact.
>
> > > > > On Oct 28, 1:48 am, loell <[email protected]> wrote:
>
> > > > > > hi, being used to the development's server, handling of memcache, 
> > > > > > and
> > > > > > that memcache items stays as long as it can.  I'm really puzzled why
> > > > > > some of my items returns "None" while part of that particular
> > > memcache-
> > > > > > set is still retrievable on the production server.   is this normal?
>
> > --
> > Nick Johnson, Developer Programs Engineer, App Engine
> > Google Ireland Ltd. :: Registered in Dublin, Ireland, Registration Number:
> > 368047
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