[continuations]

How big is your largest customer though?

You can easily buy a machine with several TB of RAM, several hundreds of TB of SSDs in RAID giving you millions of IOPS, quad-socket 256 cores. How likely is it that a single machine cannot handle a single customer?

[jjeaff]

Ya, this is always what I think about when I see people spending lots of effort on "scalability".

You either need an enormous client base or are doing something very specialized that requires tons of memory or cpu per customer.

I would think 99% of all internet companies could likely handle everything on a single massive machine, or two, for redundancy. Assuming they were somewhat optimized.

[derekperkins]

That introduces different problems. Applying MySQL replication logs is single threaded by default and generally doesn't scale as well as the master, so it becomes increasingly difficult to keep replicas from lagging.

As your database gets into tens or hundreds of TBs, now backups and restores take hours or days to complete. Any DR scenario becomes an existential threat.

For large tables, schema changes can take weeks. This often results in developers doing their own custom table sharding strategies, even though they might still be on a single machine.

I'm not saying that you can't architect around these problems, but operating a db at massive scale on a single machine isn't the obvious win that it seems to be.