Hi Kim, It's not clear from your description exactly how you're performing your tests. Without extra information, the most likely explanation would be that you're seeing a race condition in your code, where the key is modified between subsequent requests to the memcache API.
Also, are you running this against the dev_appserver, or in production? -Nick Johnson On Tue, Jun 23, 2009 at 7:18 AM, Kim Riber <kimsteenri...@gmail.com> wrote: > > Just made another test, to confirm the behavior I see. > This example is much simpler, and simply has 10 threads writing random > values to memcahce to the same key. > I would expect the last value written to be the one left in memcache. > When afterwards, having 4 threads reading 10 times from that same key, > they return 2 different values. > This only happens if I prior to the writing threads, run some heavy > tasks, to force gae to spawn more app instances. > It seems like each server cluster might have its own memcache, > independant from each other. I hope this is not true. From a thread > from Ryan > > http://groups.google.com/group/google-appengine/browse_thread/thread/45272062a8e36545/2289806f3f711c09?lnk=gst&q=memcache+atomic#2289806f3f711c09 > he states that > > >as for the datastore, and all other current stored data APIs like > >memcache, there is a single, global view of data. we go to great > >lengths to ensure that these APIs are strongly consistent. > > Regards > Kim > > On Jun 17, 8:51 pm, Kim Riber <kimsteenri...@gmail.com> wrote: > > To clarify a bit: > > > > one thread from our server runs one loop with a unique id. > > each requests stores a value in memcache and returns that value. In > > the following request, the memcache is queried if the value just > > written, is in the cache. > > This sometimes fail. > > > > My fear is that it is due to the requests changing to another app > > instance and then suddently getting wrong data. > > > > instance 1 +++++ +++++ > > instance 2 -- > > > > Hope this clears out the example above a bit > > > > Cheers > > Kim > > > > On Jun 17, 7:52 pm, Kim Riber <kimsteenri...@gmail.com> wrote: > > > > > Hi, > > > I'm experiencing some rather strange behavior from memcache. I think > > > I'm getting different data back from memcache using the same key > > > The issue I see is that when putting load on our application, even > > > simple memcache queries are starting to return inconsistant data. When > > > running the same request from multiple threads, I get different > > > results. > > > I've made a very simple example, that runs fine on 1-200 threads, but > > > if I put load on the app (with some heavier requests) just before I > > > run my test, I see different values coming back from memcache using > > > the same keys. > > > > > def get_new_memcahce_value(key, old_value): > > > old_val = memcache.get(key) > > > new_val = uuid.uuid4().get_hex() > > > reply = 'good' > > > if old_val and old_value != "": > > > if old_val != old_value: > > > reply = 'fail' > > > new_val = old_value > > > else: > > > if not memcache.set(key, new_val): > > > reply = 'set_fail' > > > else: > > > reply = 'new' > > > if not memcache.set(key,new_val): > > > reply = 'set_fail' > > > return (new_value, reply) > > > > > and from a server posting requests: > > > > > def request_loop(id): > > > key = "test:key_%d" % id > > > val, reply = get_new_memcahce_value(key, "") > > > for i in range(20): > > > val,reply = get_new_memcahce_value(key, val) > > > > > Is memcache working localy on a cluster of servers, and if an > > > application is spawned over more clusters, memcache will not > > > propergate data to the other clusters? > > > > > I hope someone can clarify this, since I can't find any post regarding > > > this issue. > > > > > Is there some way to get the application instance ID, so I can do some > > > more investigation on the subject? > > > > > Thanks > > > Kim > > > > > > > -- Nick Johnson, App Engine Developer Programs Engineer Google Ireland Ltd. :: Registered in Dublin, Ireland, Registration Number: 368047 --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Google App Engine" group. To post to this group, send email to google-appengine@googlegroups.com To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en -~----------~----~----~----~------~----~------~--~---
