Ecto Migration lock and DDL transaction support

[dbernheisel]

I noticed that this adapter doesn't seem to support DDL transactions or a migration lock during ecto migrations. Does that support need to be implemented?

I'm probably missing something, but I figure that a DDL transaction can be started with exclusive mode, and perhaps the migration lock is satisfied with a file lock?

https://github.com/elixir-sqlite/ecto_sqlite3/blob/main/lib/ecto/adapters/sqlite3.ex#L218-L224

I'll be happy to contribute if there's a clear way forward.

[warmwaffles]

I don't know if SQLite actually supports DDL transactions, but like you said, we could "fake" it with exclusive. I didn't implement it because ecto sqlite 2 did not implement it.

[recursiveGecko]

I don't know if SQLite actually supports DDL transactions

ALTER TABLE documentation confirms that it does, as well as this simple demo:

Having support for DDL transactions would be really appreciated!

[warmwaffles]

I'll take a look into this. I'll check if there is some upstream integration tests that test the DDL transactions and see if we can get that implemented.