Ractor safety

[HoneyryderChuck]

👋 I am using sequel for this tool I'm working on, where there's a pool of workers, each using the default connection pool to pick a connection tu use. Recently, I've been toying with the idea of adding support for a pool of ractors. In order to make it work though, sequel would need to at least be ractor-safe, which is not at the moment.

The first issue is that database instances, even if frozen, aren't shareable:

DB = Sequel.connect("...")

Ractor.new(DB) do |db|
   # does not work, because Sequel::Database does not implement #initialize_copy

This can be overcome by initializing the database instance within the ractor:

Ractor.new do
  db = Sequel.connect("...")

But then all other sorts of issues happen, the first of which is, using ADAPTER_MAP when connecting fails, as it's a mutable constant.

I've made a local patch to ditch its usage and rely on Sequel::Database.subclasses.find and .adapter_scheme. I believe the scheme cache of ADAPTER_MAP optimizes a cold path (connecting happens usually once per database URL, and there aren't usually many of them). There's of course the open question of what to do with the double declaration of the postgres adapter overriding the scheme, I guess this is for backwards-compatibility?

And this is just the beginning: Sequel.synchronize is used liberally in a few places, and is definitely not ractor-friendly; moreover, sequel caches a lot of method-to-proc coercers, which aren't themselves ractor-shareable I've created an issue in ruby about whether these procs should be considered exceptions.

---

This is the summary of early discovery. I don't know how much Jeremy is interested in making sequel work under ractors, and while I believe that it's going to take a lot of effort making the whole of sequel ractor-friendly, I wonder how much one has to do in order to make the vanilla "no-plugin" XP usable.

Is this something worth undertaking, or a rabbit-hole someone may have gone through in the past already?

[jeremyevans]

With current limitations of Ractor, I don't think there is any chance of Sequel being able to use it. If you want thread-level parallelism when using Sequel, I recommend using JRuby.