ctlstore VS sqlite

We replicated our MySQL database to a SQLite edge at Segment in ctlstore: https://github.com/segmentio/ctlstore

We considered tailing binlogs directly but there's so much cruft and complexity involved trying to translate between types and such at that end, once you even just get passed properly parsing the binlogs and maintaining the replication connection. Then you have to deal with schema management across both systems too. Similar sets of problems using PostgreSQL as a source of truth.

In the end we decided just to wrap the whole thing up and abstract away the schema with a common set of types and a limited set of read APIs. Biggest missing piece I regret not getting in was support for secondary indexes.

> it is only practical for situations where the write rate (<100/s total) and data volumes (<10GB total) are low.

This comment from the GitHub project page is pretty important. Configuration data often sees slow change, and isn't huge so a custom approach seems viable. I wonder how close they are to that 100/s ceiling.

There's also an unmentioned transition to eventual consistency happening here:

> The implications of this decoupling is that the data at each instance is usually slightly out-of-date (by 1-2 seconds).

> The reader API provides a way to fetch an approximate staleness measurement that is accurate to within ~5 seconds.

That's could lead to more complex application logic or risk of confusing users with stale behavior. No free lunch here.

[1] https://segment.com/blog/separating-our-data-and-control-pla...

[2] https://github.com/segmentio/ctlstore

at segment we benchmarked https://github.com/segmentio/ctlstore against this driver. We saw about a 50% hit to read performance, so we didn't move forward with it, but the improvements in service build times were really appealing.

> I would've probably picked the modernc variation

Heads up about the modernc library, it has been stuck on an old version of sqlite for several months [1]. It seems like maintainer time is the limiting factor [2]. There has been a call to arms on that issue page, the maintainer is looking for help, but it looks like not much has arrived. It seems like it might trace back to blockers in the C-to-Go compiler.

It's a major undertaking and a very impressive piece of work, but I'm not surprised it's a struggle when big roadblocks get hit. I hope they find a way to progress, but I'm very relieved to be seeing some CGo-free alternatives like ncruces/go-sqlite3 emerging. I'm going to give it a try for sure and see if I can live with the compromises.

Squinn-go looks very compelling too, but I don't like that it requires the squinn binary to already be installed on a user's machine, I think that gives with one hand and takes with the other: sure, I get to avoid CGo, but I also lose the turnkey, single-command install, static build benefits Go brings out of the box.

Seconding the point about nitty gritty, I'd read it for sure too!

  [1]: https://gitlab.com/cznic/sqlite/-/issues/154

No, but that has the disadvantage of being C compiled into Go, then being compiled into native executable.

I'm actually surprised by how readable this came out; props to the Go->C compiler author. But you can guess that pushing this sort of thing through the Go compiler is going to cause some slowdowns due to sheer paradigm mismatch: https://gitlab.com/cznic/sqlite/-/blob/master/lib/sqlite_lin...

FWIW, we use a version of SQLite transpiled into Go to avoid CGI problems: https://gitlab.com/cznic/sqlite

It could be clearer in the readme, but note that this is a machine translation from C to Go, repeated for every OS-Arch pair. Example of the one you're most likely to use in production: https://gitlab.com/cznic/sqlite/-/blob/master/lib/sqlite_linux_amd64.go