Horizontal sharding & migration with data changing script #42873

Hello folks and @eileencodes

I was trying the Horizontal sharding and couldn't go through this. Thanks for your job anyway 👍

Steps to reproduce

git clone https://github.com/alpracka/sharding_migrations
cd sharding_migrations && bundle
bin/rails db:create
bin/rails db:migrate

Expected behavior

Migrations should be finished on all databases.

Actual behavior

Migration with data changing script is not finished and goes to zombie mode.

Few notes:

• No matter if the script is written like reversible block or def up/down methods.
• PostgreSQL:
  It just hangs out like on the gif below.
• SQLite:
  It seems to work but doesn't work if there are some records in the database. But it seems to be a different issue as reset_column_information doesn't work in this case 🤷‍♂️.
• MySQL:
  All migrations are finished but the data changing script is performed only on the primary database because all Animal records in the primary_shard_one database have nil value of the attribute lives.

System configuration

Rails version: 6.1.4 (I also tried the main branch with same results)

Ruby version: 3.0.1