One database per customer, or one database for the whole SaaS-app?

For someone coming from the classic client-server model of software development it can be hard to switch an app from serving a single customer to distributing it as an SaaS-app.

Can I have one database per customer?

Sure. I have seen multiple variants of this. It is an easy way of transitioning and old app built with client-server model to a SaaS-version. You just set up a new database for each customer installation.

I have seen use cases where tens of thousands of customers has their own database.

There are some benefits to this model.

  • A database can be corrupted and it affects only one customer.
  • You can upgrade a few of your customers to a new version of the app and move one customer at a time. If something breaks, the first customers will let you know.
  • You can move specially important customers to dedicated servers with more bandwidth and better performance.
  • It is easier to implement custom changes for specific clients
  • A database with a smaller number of records is much faster
  • Restoring lost data for a single client is easy - just restore the whole database backup for that client.
  • Wider range of choice when picking a database. With different databases for each customer even SQLite may be an option, but you will probably need one of the big players if you are going to share the database.
  • Your code will be simpler since you never have to check for client ownership of a record in the database.

But there are also some drawbacks:

  • Updating the database schemas will be a pain, even with a good script.
  • Handling all the database connections will require better hardware than an equivalent solution sharing a database.
  • Bugs coming from differences in the databases will be hard to track and test
  • Getting statistics from all your customers will be hard using only the database console
  • Row ID:s could be a source of problems when they are reused across the databases and later exposed via an API.

What are you suggesting?

For new apps, I tend to go with a shared database. Migrating to newer versions are relatively easy and scaling is easy in the beginning. If I get to a point where I feel that multiple databases are the best solution I normally have enough customers on the app to justify spending a couple of days on the migration.

I also like to spend more time in the code and less time managing databases.

When would you go with multiple databases?

There are some cases that would make me consider having one database per customer:

  • If you have an existing app that is built for a single customer and don’t want to add ClientID to all database columns - and code to handle security.
  • If you will be offering a lot of customizations to the app
  • If you will offer installs on customer hardware.
  • If you will have a HUUUGE user base or they will store huge datasets.
  • If your app handles really sensitive data