Should I use files or a database?

Question

I'm building a cloud sync application which syncs a users data across multiple devices. I am at a crossroads and am deciding whether to store the data on the server as files, or in a relational database. I am using Amazon Web Services and will use S3 for user files or their database service if I choose to store the data in a table instead. The data I'm storing is the state of the application every ten seconds. This could be problematic to be storing in a database because the average number of rows per user that would be stored is 100,000 and with my current user base of 20,000 people that's 2 billion rows right off the bat. Would I be better off storing that information in files? Because that would be about 100 files totaling 6 megabytes per user.

Answer 1

As discussed in the comments, I would store these as files.

S3 is perfectly suited to be a key/value store and if you're able to diff the changes and ensure that you aren't unnecessarily duplicating loads of data, the sync will be far easier to do by downloading the relevant files from S3 and syncing them client side.

You get a big cost saving of not having to operate a database server that can store tonnes of rows and stay up to provide them to the clients quickly.

My only real concern would be that the data in these files can be difficult to parse if you wanted to aggregate stats/data/info across multiple users as a backend or administrative view. You wouldn't be able to write simple SQL queries to sum up values etc, and would have to open the relevant files, process them with something like awk or regular expressions etc, and then compute the values that way.

You're likely doing that on the client side any for the specific files that relate to that user though, so there's probably some overlap there!