Yet another consideration - you need to be aware that when you raise multiple tasks in quick succession, it is possible (likely even) that they will execute concurrently. If each task is trying to update the same entity, they may very well compete with each other, and enter a contention/retry deadlock.
On Oct 28, 11:33 pm, hawkett <hawk...@gmail.com> wrote: > One possible consideration - when you raise multiple tasks, do you do > so in a single call to the task queue API (batch put) or multiple > calls? If the latter, a great test would be to change to batch put and > see if the problem goes away. > > On Oct 28, 11:29 pm, hawkett <hawk...@gmail.com> wrote: > > > > > > > > > Hi Matija, > > > I can see your use case - you want to make sure that either all > > tasks get raised, or none. I can also see your worry - that tasks are > > actually being *fired* before the transaction is complete. I agree > > this would be a completely incorrect situation. I also transactionally > > raise multiple tasks, but I always have a datastore operation in > > conjunction (and use python) - I haven't encountered this issue of > > tasks being fired before the transaction completes, but I wonder if > > google has made the assumption that a transaction will always contain > > a datastore operation, and perhaps their logic is misbehaving if it > > does not? > > > An example of how this might happen is if their logic is waiting for a > > counter of outstanding db operations to reach 0 before raising tasks. > > This would be flawed logic. Thanks, > > > Colin > > > On Oct 28, 8:21 am, Matija <matija.jerko...@gmail.com> wrote: > > > > I am not saving any entities but I am putting more than one task in > > > queue. It depends of the data that current task is processing. Let's > > > say two tasks (always less then five). > > > > At the end of 'transaction' I will have two tasks in queue or none. > > > > This usually works, but sometimes I get this > > > ConcurrentModificationException exception. Complete application chunk > > > works eventually because task with execute again and will finish > > > correctly, but it would be nice to understand this exception so that I > > > can avoid it. > > > > On Oct 28, 1:58 am, Tim Hoffman <zutes...@gmail.com> wrote: > > > > > If you are not saving any entities why are you using a transaction to > > > > put the task into the queue. > > > > > The idea of a queuing a task transactionally is that the task doesn't > > > > get fired if the transaction fails (ie you save of entities fails). > > > > > Seems completely redundant > > > > > Rgds > > > > > T > > > > > On Oct 21, 11:18 pm, Matija <matija.jerko...@gmail.com> wrote: > > > > > > Hi, > > > > > I am > > > > > usinghttp://code.google.com/appengine/docs/java/taskqueue/overview.html#Ta... > > > > > way to enqueue two tasks in transaction. But I am not saving any > > > > > datastore entities. I am using objectify. > > > > > > I got this message: > > > > > > java.util.ConcurrentModificationException: too much contention on > > > > > these datastore entities. please try again. > > > > > at > > > > > com.google.appengine.api.datastore.DatastoreApiHelper.translateError(Datast > > > > > oreApiHelper.java: > > > > > 39) > > > > > at > > > > > com.google.appengine.api.datastore.DatastoreApiHelper.makeSyncCall(Datastor > > > > > eApiHelper.java: > > > > > 75) > > > > > at > > > > > com.google.appengine.api.datastore.TransactionImpl.makeSyncCall(Transaction > > > > > Impl.java: > > > > > 44) > > > > > at > > > > > com.google.appengine.api.datastore.TransactionImpl.makeSyncCall(Transaction > > > > > Impl.java: > > > > > 52) > > > > > at > > > > > com.google.appengine.api.datastore.TransactionImpl.commit(TransactionImpl.j > > > > > ava: > > > > > 64) > > > > > > When this happened only one task needed to be added to queue, so why > > > > > this error ? -- 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-appeng...@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.
