18bytes 18bytes - 1 month ago 10
Python Question

Concurrent requests in Appengine Python

Official appengine documentation says that if we set threadsafe property to true in app.yaml then appengine will server concurrent requests.

Official link:
https://developers.google.com/appengine/docs/python/python27/newin27#Concurrent_Requests


  • Does it mean application will be faster (than 2.5) if we have threadsafe property to true? Official documentation/blog says so but i am looking for real world experiences.

  • At highlevel, How does it work internally? Will our application be initialized and spawn a new theread for each request?


Answer Source

You still only have one thread per request - you can't spawn.

With threadsafe off, Appengine will only route one request to an instance. So if the number of requests per second times the time to handle a request approaches one, Appengine will spin up a new instance to handle them. This cost money. With threadsafe on, Appengine can route more than one request to an instance.

Whether this helps you or not depends on your app and your traffic:

  1. First, calculate inbound request per second / average latency. If this is well under one, threadsafe won't make much difference either way.
  2. Examine your app to find out how much time it spends waiting on APIs (datastore or URL fetch for instance). If this is a large proportion, then threadsafe will help keep your instance count down. If not, it won't help much.

The simple rule is switch threadsafe on unless your app is very processing-intensive (little API waiting).