[jitl]

Multi-tenant design is a huge win in terms of reducing developer toil and expense.

Many customers will have a tiny amount of data. For those customers a dedicated database is huge amount of overhead. There may not be any single customer who it makes sense to allocate dedicated "hardware" for.

Sure you have to deal with a one-time pain to shard your thingy, but you don't need to pay for tens-of-thousands of individual database servers, write interesting tools to keep their schemas in sync, wrangle their backups, etc.

[giva]

I don't mean one database server for each customer. I say one database for customer. Hundreds or thousands of customer can be on the same database server. When you need more resources, you add another server. If customer grows too much, you move it on another server.

There is a bit of overhead, but not huge by any means.

Being able to update schema one customer at a time is a huge plus in my view, as it gives you a lot of flexibility in rollout. You deploy a new version of the application on a new application server and move the customers on the new servers updating their schema one by one (automatically, obviously)

Backups are routinely automated anyway.

[davitocan]

I've done this before where we ran a schema per customer and it was fabulous. Once the customer was large enough we could justify allocating a separate DB for them. The application was written in such a way that it knew which data store to query based on the user.