Thanks for the detail - pretty comfortable with the ins and outs of the task queue - any ideas about the 5 task limit?
> Also, don't confuse transactional tasks with the task queue. Transactional > tasks are the those that will all happen simultaneously or will graciously > fail without any partial commits. Due to the implementation details you > probably want to avoid intentionally doing lots of transaction updates on > the same few objects, since it is possible (if you are kicking lots of > simultaneous jobs off with the task queue) to shoot yourself in the foot and > have a very small success rate. I wasn't confused until I read this paragraph :) Transactional tasks do not need to operate on the same entity group as the transaction in which they are raised - this is one of their greatest strengths. They are fast to raise, so you can actually include quite a lot of work in a 'transaction' of this sort, all done in parallel. Generally if I want to do something in the same entity group as the originating transaction, I would do it right there in the transaction and not raise a task. So at least for me (and I expect for many others), transactional tasks are almost exclusively *not* operating on the same entity group as the transaction in which they are raised, unless perhaps they are being used in a continuation style bulk update, in which case they are likely to be in series and not cause contention. Anyway, question still there :) Is the 5 task limit a restriction that is expected to remain indefinitely? Can I get around the restriction by raising more in a single batch API call - i.e. is it a restriction on API calls or actual tasks? Cheers, Colin On Jul 7, 4:46 pm, Nate Bauernfeind <[email protected]> wrote: > I have noticed that batch datastore calls run within a single transaction. > The maximum number of entities that can be added or deleted (and probably > modified, though I have not tried) was 500. I'm betting you could probably > wrap them around a single transaction. Though, from my experience, I > wouldn't really recommend doing this (since trying to commit two batches of > 500 to the datastore within the same call tended to time out for me). > > Also, don't confuse transactional tasks with the task queue. Transactional > tasks are the those that will all happen simultaneously or will graciously > fail without any partial commits. Due to the implementation details you > probably want to avoid intentionally doing lots of transaction updates on > the same few objects, since it is possible (if you are kicking lots of > simultaneous jobs off with the task queue) to shoot yourself in the foot and > have a very small success rate. > > Transactions work with the task queue in such a way that the task will only > be added to the queue if no other piece of your commits fail. For example, > you wouldn't really want your app to run the "new user" code if you couldn't > create the new user account for that user because someone else registered > that user name at the same time. I.E. Things on the task queue do not > continue running within the same transaction if they were created within > one. > > > > On Wed, Jul 7, 2010 at 4:22 AM, hawkett <[email protected]> wrote: > > Hi, > > > This page - > >http://code.google.com/appengine/docs/python/datastore/transactions.html > > - says that we cannot raise more than 5 transactional tasks in a > > single transaction, and I wanted to check if this was a limit that you > > were hoping to raise, or if this is likely to be a long term > > restriction? Does this restriction limit API calls to the task queue > > or actual number of tasks - e.g. could I raise more than 5 by doing > > them in batch with a single call to the task queue API? Cheers, > > > Colin > > > -- > > You received this message because you are subscribed to the Google Groups > > "Google App Engine" group. > > To post to this group, send email to [email protected]. > > To unsubscribe from this group, send email to > > [email protected]<google-appengine%2Bunsubscrib > > [email protected]> > > . > > For more options, visit this group at > >http://groups.google.com/group/google-appengine?hl=en. -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
