Consecutive XML HTTP Requests seem to block on Google App Engine

I am working on an application on Google App Engine. Roughly this is what I do: The user screen is split into 2 parts (actually 3, but lets leave that out for now). The left part (this takes upto 75% of the screen) has a document with some words highlighted. When one of these highlighted words are clicked the right part displays various meanings of it, example usage etc. The way this works is clicking the word send an XML HTTP Request to the server, where the sample usage(s)/meaning(s) are retrieved from the datastore. This data is returned and displayed.

My problem:

After I click on a few words consecutively, the application seems to "hang" - say, I click on 5 words in quick succession, clicking开发者_运维百科 on the 6th word (or any word after that) doesn't replace the info regarding the 5th word on my right panel.

Since some data store columns (at least single valued properties) are indexed by default I'm guessing retrieval is not the bottleneck here. It is probably the requests.

Is such an issue known with the GAE? Any workarounds possible?

Kind of in a soup with this - the application was supposed to go live today. Urgent help required!

Thanks! :)

You're probably being limited to two simultaneous requests by your browser - not by appengine. If you click on a third link before the first two have had a chance to return, make sure your app can deal with requests returning for links that should no longer be displayed.

If you were hitting a limit on appengine, you'd see exceptions in your server logs. If you're not seeing those exceptions, it's probably a client-side issue.

Sorry for the late ack (for some reason I received a notification for the responses a day late, by which we had managed to fix a few things). It does look like the problem was at the data end - our code was doing some inserts, and it turns out you can't do too many of them quickly - the logs reported a transaction time-out error. The reason we couldn't spot it earlier in the logs was we were writing simply too much info out and this was buried in somewhere.

The clicks on the user-side were pulling data from this table.

Unfortunately, the GAE simulator doesn't simulate any timeout error - so even though we had tested with comparable volumes of data before deployment this error never happened during development.

Thanks again for your responses! And yet again, I apologize for responding late.