Show HN: Restate – Low-latency durable workflows for JavaScript/Java, in Rust

You can absolutely do something similar with a RDBMS.

I tend to think of building services in state machines: every important step is tracked somewhere safe, and causes a state transition through the state machine. If doing this by hand, you would reach out to a DBMS and explicitly checkpoint your state whenever something important happens.

To achieve idempotency, you'd end up peppering your code with prepare-commit type steps where you first read the stored state and decide, at each logical step, whether you're resuming a prior partial execution or starting fresh. This gets old very quickly and so most code ends up relying on maybe a single idempotency check at the start, and caller retries. You would also need an external task queue or a sweeper of some sort to pick up and redrive partially-completed executions.

The beauty of a complete purpose-built system like Restate is that it gives you a durable journal service that's designed for the task of tracking executions, and also provides you with an SDK that makes it very easy to achieve the "chain of idempotent blocks" effect without hand-rolling a giant state machine yourself.

You don't have to use Restate to persist data, though you can - and you get the benefit of having the state changes automatically commit with the same isolation properties as part of the journaling process. But you could easily orchestrate writes into external stores such as RDBMS, K-V, queues with the same guaranteed-progress semantics as the rest of your Restate service. Its execution semantics make this easier and more pleasant as you get retries out of the box.

Finally, it's worth mentioning that we expose a PostgreSQL protocol-compatible SQL query endpoint. This allows you to query any state you do choose to store in Restate alongside service metadata, i.e. reflect on active invocations.

Super excited to hear what you do with it though!