reshape VS gh-ost

Cool stuff! Do you have any thoughts about how this compares to https://github.com/fabianlindfors/reshape?

From what I know, there is only one project that tries something close to this: the relatively recent Reshape. It uses Postgres views to expose the two versions of the schema and triggers to upgrade/downgrade the new data. It doesn’t do the constraints part as described above, but shows that this approach is possible. Combined with the Xata pull request based workflow, I think the ideal system described above is possible!

My idea is not unique. Reshape is similar, but bigger in scope.

This is precisely what I did for my automated zero-downtime migration tool and it works pretty well: https://github.com/fabianlindfors/reshape. At least for Postgres, simple views like these have almost no overhead as queries are simply rewritten for the underlying table.

Anybody interested in this subject might also be interested in a tool for Postgres I’ve been working on, Reshape: https://github.com/fabianlindfors/reshape. It aims to fully automate away all the pain and manual steps zero-downtime migrations normally requires :)

This post is absolutely terrific and has been been my main reference for Reshape, an automated, zero-downtime schema migration tool: https://github.com/fabianlindfors/reshape

I’ve been through multiple incidents where everything worked fine in the testing environment but ended up locking the production database for minutes when deployed. A category of open-source tools called OSC (Online Schema Change) exists to mitigate such pain, like gh-ost used by GitHub and OSC used by Meta. They work by creating a set of "ghost tables" to apply the migrations, copy over old data from the original tables, and catch up with new writes simultaneously. When all old data is migrated, you can trigger a cutover to make the "ghost tables" production. Check the post below for a great introduction and comparison:

Sounds like it's basically explained in the gh-ost readme https://github.com/github/gh-ost#how

I think it amounts to "use views to decouple access to the table with a fixed interface" and "use triggers for migrating data between tables"

Gh-ost is the new hotness. Simple to use and lots of great features: https://github.com/github/gh-ost

If the performance of the db is a concern during migrations (locking, high cpu consumption for large writes) there are tools that can help and do similiar to what your describing but with the benefit that they are battle tested tools. This one spring to mind https://github.com/github/gh-ost there are other options as well and its worth reading the trade off docs

Not sure which version of MySQL you're using, but one approach would be to use a tool like pt-online-schema-change (from Percona) or g-host -- which will create a duplicate table and then swap it in place of the original table. It's a safer approach when operating in production environments. Here's a good comparison of the tools many people use https://planetscale.com/docs/learn/online-schema-change-tools-comparison

No, especially on large tables with billions of records. They make online schema changes impossible. More details: https://github.com/github/gh-ost/issues/331#issuecomment-266...

Tip #4: Consider slow-running migrations. Some tables can be so large that the traditional migration way is simply not a viable option for them. In such cases, you can consider embedding the data migration code right into your application, or use a special utility like GitHub's online schema migration for MySQL. A slow-running migration can work in production for days or even weeks. It gradually converts the data by small chunks, so you can carefully balance the load on the database while making sure that it doesn't cause slowness or downtime.

GitHub gh-ost

Actually I never tried but I was scared by the small print of GH not using RDS themselves [1] and Ghost relying on lower-level features that might be not easily available in RDS. Also I had the impression you have to setup a normal non-RDS replica attached to your RDS master?

[1] https://github.com/github/gh-ost/blob/master/doc/rds.md