pgroll VS tusker

My thoughts exactly. It's surprising that external online schema change tools for Postgres have only become a thing fairly recently! The only two I'm aware of are:

* pgroll: Written in Golang, first commits June 2023. https://github.com/xataio/pgroll

* pg-osc: Written in Ruby, first commits Dec 2021. https://github.com/shayonj/pg-osc

Meanwhile over in the MySQL and MariaDB ecosystem, external OSC tools have been around for quite some time, starting with oak-online-alter-table over 15 years ago. The most popular options today are pt-online-schema-change or gh-ost, but other battle-tested solutions include fb-osc, LHM, and the latest entry Spirit.

I thought I recognized xataio - they submitted pgroll a few months back https://news.ycombinator.com/item?id=37752366 (https://github.com/xataio/pgroll - Apache 2)

At the start of October we released pgroll, an open source tool for zero-downtime, reversible schema migrations for Postgres.

If you have any suggestions or questions, please open an issue in our GitHub repo, reach out to us on Discord or follow us on X / Twitter. We'd love to hear from you and keep you up to date with the latest progress on pgroll.

Any pgroll operations[0] that require a change to an existing column, such as adding a constraint, will create a new copy of the column and backfill it using 'up' SQL defined in the migration and apply the change to that new column.

There are no operations that will modify the data of an existing column in-place, as this would violate the invariant that the old schema must remain usable alongside the new one.

[0] - https://github.com/xataio/pgroll/tree/main/docs#operations-r...

This is a fantastic article! It shows that even simple migrations (like adding or removing a column) can be quite tricky to deploy in concert with the application deployement.

We (at Xata) have tried for a while to come up with a generic schema migration system for PostgreSQL that makes this easier. We ended up using views and temporary columns in such a way that we can provide both the "old" and the "new" schema simultaneously. Up/down triggers convert newly inserted data from old to new and the other way around. This also has the advantage the it can do rollbacks instantly by just dropping the "new" view.

We were just planning to announce this as an open source project this week, but actually it is already public, so if you are curious: https://github.com/xataio/pgroll

Thanks! Yeah definitely agree that building out declarative table management for Postgres would be a major effort. A few open source projects I've seen in that area include:

https://github.com/sqldef/sqldef (Go)

https://github.com/bikeshedder/tusker (Python but being ported to Rust)

https://github.com/tyrchen/renovate (Rust)

https://github.com/blainehansen/postgres_migrator (Rust)

Some of these are based on parsing SQL, and others are based on running the CREATEs in a temporary location and introspecting the result.

The schema export side can be especially tricky for Postgres, since it lacks a built-in equivalent to MySQL's SHOW CREATE TABLE. So most of these declarative pg tools shell out to pg_dump, or require the user to do so. But sqldef actually implements CREATE TABLE dumping in pure Golang if I recall correctly, which is pretty cool.

There's also the question of implementing the table diff logic from scratch, vs shelling out to another tool or using a library. For the latter path, there's a nice blog post from Supabase about how they evaluated the various options: https://supabase.com/blog/supabase-cli#choosing-the-best-dif...

Big fan of tusker (https://github.com/bikeshedder/tusker) for PostgreSQL migrations. Tusker takes a SQL-first approach; You write your schema in declarative DDL (I have my entire project in one schema.sql file) and when you edit it, tusker generates the sql code required to migrate. It uses temporary test databases to run both your declarative DDL and your step-by-step migrations to ensure they are in lock step. And it can connect to live databases and diff your schema/migrations against reality. I've never seen a better toolkit for schema evolution.

Forr postgres, how does the schema diffing aspect compare to migra?

https://github.com/djrobstep/migra

I'm asking because, although migra is excellent and there are multiple migrations tools based on it (at least https://github.com/bikeshedder/tusker and https://github.com/blainehansen/postgres_migrator), issues are piling up but development seem to be slowing down

Is this similar to migra? There's a tool written in Rust that calls it, postgres_migrator (there's also tusker)

The best solution I've ever seen is this Rust library https://github.com/cornucopia-rs/cornucopia

You write plain SQL for you schema (just a schema.sql is enough) and plain SQL functions for your queries. Then it generates Rust types and Rust functions from from that. If you don't use Rust, maybe there's a library like that for your favorite language.

Optionally, pair it with https://github.com/bikeshedder/tusker or https://github.com/blainehansen/postgres_migrator (both are based off https://github.com/djrobstep/migra) to generate migrations by diffing your schema.sql files, and https://github.com/rust-db/refinery to perform those migrations.

Now, if you have simple crud needs, you should probably use https://postgrest.org/en/stable/ and not an ORM. There are packages like https://www.npmjs.com/package/@supabase/postgrest-js (for JS / typescript) and probably for other languages too.

If you insist on an ORM, the best of the bunch is prisma https://www.prisma.io/ - outside of the typescript/javascript ecosystem it has ports for some other languages (with varying degrees of completion), the one I know about is the Rust one https://prisma.brendonovich.dev/introduction

> Tusker actually uses Migra to power its functionality: https://github.com/bikeshedder/tusker#how-does-it-Work

What a twist! Might we ask what field you work in? Seems niche