How to create a multi-tenant database with shared table structures?

Question

Our software currently runs on MySQL. The data of all tenants is stored in the same schema. Since we are using Ruby on Rails we can easily determine which data belongs to wh

Answer 1

My experience (albeit SQL Server) is that multi-database is the way to go, where each client has their own database. So although I have no mySQL or Ruby On Rails experience, I'm hoping my input might add some value.

The reasons why include :

1. data security/disaster recovery. Each companies data is stored entirely separately from others giving reduced risk of data being compromised (thinking things like if you introduce a code bug that means something mistakenly looks at other client data when it shouldn't), minimizes potential loss to one client if one particular database gets corrupted etc. The perceived security benefits to the client are even greater (added bonus side effect!)
2. scalability. Essentially you'd be partitioning your data out to enable greater scalability - e.g. databases can be put on to different disks, you could bring multiple database servers online and move databases around easier to spread the load.
3. performance tuning. Suppose you have one very large client and one very small. Usage patterns, data volumes etc. can vary wildly. You can tune/optimise easier for each client should you need to.

I hope this does offer some useful input! There are more reasons, but my mind went blank. If it kicks back in, I'll update :)

EDIT:
Since I posted this answer, it's now clear that we're talking 10,000+ tenants. My experience is in hundreds of large scale databases - I don't think 10,000 separate databases is going to be too manageable for your scenario, so I'm now not favouring the multi-db approach for your scenario. Especially as it's now clear you're talking small data volumes for each tenant!

Keeping my answer here as anyway as it may have some use for other people in a similar boat (with fewer tenants)