App Engine: Few big scripts or many small ones?

Question

I am working on a website that I want to host on App Engine. My App Engine scripts are written in Python. Now let\'s say you could register on my website and have a user pro

Answer 1

A single big script would have to be loaded every time an instance for your app starts, possibly hurting the instance start time, the response time of every request starting an instance and the memory footprint of the instance. But it can handle any request immediately, no additional code needs to be loaded.

Multiple smaller scripts can be lazy-loaded, on demand, after your app is started, offering advantages maybe appealing to some apps:

• the main app/module script can be kept small, which keeps the instance startup time short
• the app's memory footprint can be kept smaller, handler code in lazy-loaded files is not loaded until there are requests for such handlers - interesting for rarely used handlers
• the extra delay in response time for a request which requires loading the handler code is smaller as only one smaller script needs to be loaded.

Of course, the disadvantage is that some requests will have longer than usual latencies due to loading of the handler scripts: in the worst case the number of affected requests is the number of scripts per every instance lifetime.

Updating a user profile is not something done very often, I'd consider it a rarely used piece of functionality, thus placing its handlers in a separate file looks appealing. Splitting it into one handler per file - I find that maybe a bit extreme. It's really is up to you, you know better your app and your style.

From the GAE (caching) infra perspective - the file quota is 10000 files, I wouldn't worry too much with just ~100 files.

Answer 2

Adding to Dan Cornilescu’s answer, writing/saving an instance to the database re-writes to the whole instance (i.e. all its attributes) to the database. If you’re gonna use put() multiple times, you’re gonna re-write the who instance multiple times. Which, aside from being a heavy task to perform, will cost you more money.

Answer 3

The are two important considerations here.

1. The number of roundtrip calls from the client to the server.

One call to update a user profile will execute much faster than 5 calls to update different parts of user profile as you save on roundtrip time between the client and the server and between the server and the datastore.

2. Write costs.

If you update 5 properties in a user profile and save it, and then update 5 other properties and save it, etc., your writing costs will be much higher because every update incurs writing costs, including updates on all indexed properties - even those you did not change.

Instead of creating a huge user profile with 50 properties, it may be better to keep properties that rarely change (name, gender, date of birth, etc.) in one entity, and separate other properties into a different entity or entities. This way you can reduce your writing costs, but also reduce the payload (no need to move all 50 properties back and forth unless they are needed), and simplify your application logic (i.e. if a user only updates an address, there is no need to update the entire user profile).