I do like the B-tree aware grouping idea. This seems like a useful optimization for larger scan-style workloads. It helps eliminate the need to vacuum as much.

Have you considered doing other kinds of optimizations? Empty pages, free pages, etc.

I do wonder - for projects that do ultimately enforce single writer sqlite setups - it still feels to me as if it would always be better to keep the sqlite db local (and then rsync/stream backups to whatever S3 storage one prefers).

The nut I've yet to see anyone crack on such setup is to figure out a way to achieve zero downtime deploys. For instance, adding a persistent disk to VMs on Render prevents zero downtime deploys (see https://render.com/docs/disks#disk-limitations-and-considera...) which is a real unfortunate side effect. I understand that the reason for this is because a VM instance is attached to the volume and needs to be swapped with the new version of said instance...

There are so many applications where merely scaling up a single VM as your product grows simplifies devops / product maintenance so much that it's a very compelling choice vs managing a cluster/separate db server. But getting forced downtime between releases to achieve that isn't acceptable in a lot of cases.

Not sure if it's truly a cheaply solvable problem. One potential option is to use a tool like turbolite as a parallel data store and, only during deployments, use it to keep the application running for the 10 to 60 seconds during a release swap. During this time, writes to the db are slower than usual but entirely online. And then, when your new release is live, it can sync the difference of data written to s3 back to the local db. In this way, during regular operation, we get the performance of local IO and fallback onto s3 backed sqlite during upgrades for persistent uptime.

Sounds like a fraught thing to build. But man it really is hard/impossible to beat the speed of local reads!

https://aws.amazon.com/about-aws/whats-new/2024/08/amazon-s3...

https://docs.aws.amazon.com/AmazonS3/latest/userguide/condit...

The motivating question for me was less “can SQLite read over the network?” and more “what assumptions break once the storage layer is object storage instead of a filesystem?”

The biggest conceptual shift was around *layout*.

What felt most wrong in naive designs was that SQLite page numbers are not laid out in a way that matches how you want to fetch data remotely. If an index is scattered across many unrelated page ranges, then “prefetch nearby pages” is kind of a fake optimization. Nearby in the file is not the same thing as relevant to the query.

That pushed me toward B-tree-aware grouping. Once the storage layer starts understanding which table or index a page belongs to, a lot of other things get cleaner: more targeted prefetch, better scan behavior, less random fetching, and much saner request economics.

Another thing that became much more important than I expected is that *different page types matter a lot*. Interior B-tree pages are tiny in footprint but disproportionately important, because basically every query traverses them. That changed how I thought about the system: much less as “a database file” and much more as “different classes of pages with very different value on the critical path.”

The query-plan-aware “frontrun” part came from the same instinct. Reactive prefetch is fine, but SQLite often already knows a lot about what it is about to touch. If the storage layer can see enough of that early, it can start warming the right structures before the first miss fully cascades. That’s still pretty experimental, but it was one of the more fun parts of the project.

A few things I learned building this:

1. *Cold point reads and small joins seem more plausible than I expected.* Not local-disk fast, obviously, but plausible for the “many mostly-cold DBs” niche.

2. *The real enemy is request count more than raw bytes.* Once I leaned harder into grouping and prefetch by tree, the design got much more coherent.

3. *Scans are still where reality bites.* They got much less bad, but they are still the place where remote object storage most clearly reminds you that it is not a local SSD.

4. *The storage backend is super important.* Different storage backends (S3, S3 Express, Tigris) have verg different round trip latencies and it's the single most important thing in determining how to tune prefetching.

Anyway, happy to talk about the architecture, the benchmark setup, what broke, or why I chose this shape instead of raw-file range GETs / replication-first approaches / etc.