Question

I want to run a script every few seconds (4 or less) in google app engine to process user input and generate output. What is the best way to do this?

Answer 1

Run a cron job.

http://code.google.com/appengine/docs/python/config/cron.html

http://code.google.com/appengine/docs/java/config/cron.html

A cron job will invoke a URL at a
given time of day. A URL invoked by
cron is subject to the same limits and
quotas as a normal HTTP request,
including the request time limit.
.

Also consider the Task Queue – http://code.google.com/appengine/docs/python/taskqueue/overview.html