Hi Luke, First the awesome news: As of 1.4.0, many queries are implicitly asynchronous. When you call PreparedQuery.asIterable() or PreparedQuery.asIterator(), we initiate the query in the background and then immediately return. This lets you do work while the first batch of results is being fetched. And, when the first batch has been consumed we immediately request the next batch. If you're performing a significant amount of work with each Entity as you iterate you will probably see a latency win as a result of this.
Now the less awesome news: We didn't get around to making the List returned by PreparedQuery.asList() work this same magic, but you can expect this in a future release. Some deeper thoughts: The underlying RPCs between your app and the datastore fetch results in batches. We fetch an initial batch of results, and once that batch has been consumed we fetch the next batch. But, there's nothing in the API that maps to these batches - it's either a List containing the entire result set or an Iterable/Iterator that returns Entities one at a time. An API that provides async access to the individual results returned by an Iterable/Iterator (Iterator<Future<Entity>>) doesn't really make sense since you don't know which call to hasNext() is going to require a new batch to be fetched, and without that knowledge, the knowledge of what is going to trigger something "expensive", you can't really make appropriate use of an asynchronous API. Going forward, we're definitely interested in exposing these batches directly, and an explicitly async API for these batches makes a lot of sense since fetching these batches would map directly to something "expensive" on the server side. Hope this helps, Max On Fri, Nov 26, 2010 at 4:41 PM, Luke <lvale...@gmail.com> wrote: > i was taking a look at the 1.4.0 javadoc for AsyncDatastoreService. i > see the get, put and delete operations return a Future, but the > prepare methods return a naked PreparedQuery object, and it doesn't > look like PreparedQuery has any async get methods. > > does the AsyncDatastoreService not support asynchronous queries, or is > there something i'm missing? > > glad to see at lets the get and put methods are async, hoping to get > async queries too (as well as async interfaces to more services). > > -- > You received this message because you are subscribed to the Google Groups > "Google App Engine for Java" group. > To post to this group, send email to > google-appengine-j...@googlegroups.com. > To unsubscribe from this group, send email to > google-appengine-java+unsubscr...@googlegroups.com<google-appengine-java%2bunsubscr...@googlegroups.com> > . > For more options, visit this group at > http://groups.google.com/group/google-appengine-java?hl=en. > > -- You received this message because you are subscribed to the Google Groups "Google App Engine for Java" group. To post to this group, send email to google-appengine-j...@googlegroups.com. To unsubscribe from this group, send email to google-appengine-java+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine-java?hl=en.
