And we're back on a 10$ VPS.
The scaling was preemptive as it was hitting 150% CPU (out of 200%). Needed to power down to rescale.
Now it's hovering at around 200% (out of 400%). About 80kb/s and 10 disk iops.
Everything goes via a sqlite db.
But because it's sqlite it's a single writer. Everything gets batched as one transaction every 100ms. The operations on a single chunk gets squashed into a single write.
Even without the squashing sqlite can handle 10000-20000+ updates/s because of the transaction batching.
With the chunk based squashing all edits to a chunk in that 100ms window become one update, so it can scale quite well.
Btw, if I add a ' to the string, it's impossible to override by othrs. At least in the UI on Firefox, the snake still ate it.