@mscwd01
You can't be sure when the cache will be evicted. You can define an
expiration, but appengine may flush your cache at any moment (its not that
common though).
So, IMHO, always write your entities into the datastore as they get updated.
Put them into the cache and only get back to the datastore if it gets
evicted. If you do not define an expiration time it will remain cached for a
long period.
If you want a better response time for your user just put into the cache and
dispatch a task to update the datastore in background (send the object as a
payload if you do not want to rely on the cache, which can get flushed).
On Mon, Oct 3, 2011 at 6:56 PM, Ikai Lan (Google) <ika...@google.com> wrote:
> The publicly available Memcache doesn't have this functionality either, and
> it's really not as simple as you might think. What if there's a lot of data?
> Do you need a cursor? Should you lock all Memcache shards? And so forth.
>
> If you're interested in a project that does something similar, you should
> check out Redis. It's a key/value store with data structures that exists all
> in memory, where values are asynchronously flushed to disk.
>
> --
> Ikai Lan
> Developer Programs Engineer, Google App Engine
> plus.ikailan.com | twitter.com/ikai
>
>
>
> On Mon, Oct 3, 2011 at 2:29 PM, mscwd01 <mscw...@gmail.com> wrote:
>
>> That's a shame, it's a real disadvantage not having that simple
>> functionality.
>>
>> Thanks for your example, although I found it a little difficult to
>> understand it completely. Are you suggesting having an entry in the
>> cache with a key string "allKeys" which maps to a List of keys
>> belonging to all the other entities in the cache? Would this allow me
>> to iterate through the keys, saving the entity to the datastore and
>> then removing the entry from the cache?
>>
>> Also what is the "putIfUntouched" statement for?
>>
>> Thanks again
>>
>>
>>
>> On Oct 3, 9:51 pm, Bruno Fuster <brunofus...@gmail.com> wrote:
>> > I don't think so.
>> >
>> > You could create a key with all entities ids that need to be updated.
>> >
>> > Something like:
>> >
>> > public void saveEntity() {
>> >
>> > cache.put(key, entity);
>> > queue.add(withUrl("/entitiesToUpdate?id="+entity.getId()));
>> >
>> > }
>> >
>> > and then
>> >
>> > public void entitiesToUpdate(Long id) {
>> >
>> > IdentifiableValue i = cache.getIdentifiable("allKeys");
>> > List<Long> keys = i.getValue();
>> > keys.add(id);
>> >
>> > boolean put = cache.putIfUntouched("allKeys", i, keys);
>> > if (!put) {
>> > //response 409 for conflict due to concurrency so appengine will
>> > retry this later
>> > }
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> > }
>> > On Mon, Oct 3, 2011 at 5:38 PM, mscwd01 <mscw...@gmail.com> wrote:
>> > > Hey
>> >
>> > > How would one return all the values stored within the memcache?
>> > > I have tried using entrySet() and values() methods on the cache but
>> > > both result in an java.lang.UnsupportedOperationException.
>> >
>> > > Ideally, I need to return all the entities stored within the cache and
>> > > bulk save them to the datastore - is this possible?
>> >
>> > > Thanks
>> >
>> > > --
>> > > You received this message because you are subscribed to the Google
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>> >
>> > --
>> > Bruno Fuster
>>
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>>
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--
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