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Comment by phsr | Hacker News Reader

How is Google App Engine? Are there any pain points one should be aware of before using it?

No RDBMS. No SQL. No joins. That's the main adjustment for me. But after you adjust to that, it's great.

I thought NoSQL was a selling point these days?

Perhaps, but the question I was responding to was about "pain points". All I was saying is if you're coming from an RDBMS background, as I am, then there are growing pains in adjusting to using BigTable. If you don't have the time or patience to make the adjustment, then this will be a pain point. Otherwise, perhaps it's a selling point.

The 30 second per page limit can be a pain too. If you need to manipulate (i.e. validate, import, export, etc.) more than a few hundred persistent objects, you'll need to write your code to do it in chunks.

That's what Task Queue is for:

With the Task Queue API, applications can perform work outside of a user request but initiated by a user request. If an app needs to execute some background work, it may use the Task Queue API to organize that work into small, discrete units, called Tasks. The app then inserts these Tasks into one or more Queues. App Engine automatically detects new Tasks and executes them when system resources permit.

Python:

http://code.google.com/appengine/docs/python/taskqueue/overv...

Java:

http://code.google.com/appengine/docs/java/taskqueue/overvie...

The task queue has the same 30 second limit. Follow either of those links above and you'll find:

the lifetime of a single task's execution is limited to 30 seconds

You still have to do more coding to chunk the work.

Cold startup sucks - it's horrendous for Java and just bad for Python.

If you have a popular app, this isn't an issue. If you don't, it hurts.

Cold startup is almost unnoticeable for Python apps (bite my lip! see update below). On the Java side it can be an issue but, as with most things, if you dig around, you can find some acceptable workarounds.

No - I've seen 'Hello World' style apps take over 4s to cold startup. For example http://timezonetimezone.appspot.com/iscorrect?query=EST

Took 4.67s to render http://www.webpagetest.org/result/100306_5PZ7/1/details/

I monitored cold startup for a month on one of my apps and some times see 10s cold startup. http://www.webpagetest.org/result/100309_5TDW/

This is after profiling, reducing imports, caching, using app appstats, etc.

Wow, you're right. I just ran a test on one of my Python apps and found the same thing. I always assumed 4 seconds was an acceptable start up time, especially when compared with some of the Java apps I have runnning on App Engine which have often exceeded the 30 second page limit on startup and generated a DeadlineExceededException. Thanks for showing your results. I would never have known this was an issue.

They're fixing this in the future by allowing reserved instances that will always run.

Couldn't you just set up a cron job to ping your app every 15 minutes until you start getting some real traffic?

You could - but it would need to be every 1 minute. Google tears down your app after 60-90 seconds of inactivity.

Some folks have resorted to pinging every minute but Google discourages that since it ties up their resources. If everyone pinged their site once a minute then resources would never be freed....

Here's a good thread on the issue https://groups.google.com/group/google-appengine/browse_thre...

You mean besides lock-in?

There's no lock-in on the Java side. Change a few lines in jdconfig.xml, add the datanucleus-rdbms jar file, add a JDBC driver jar file and you're app will run on Tomcat or Jetty with MySQL or any database with a JDBC driver.

Check out the AppScale project: http://code.google.com/p/appscale/

You can run your App Engine apps pretty much anywhere.

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