Support force dropping database introduced in PostgreSQL 13

[ruudk]

I was getting annoyed by:

$ mix ecto.reset
** (Mix) The database for App.Repo couldn't be dropped: ERROR 55006 (object_in_use) database "app_dev" is being accessed by other users

There is 1 other session using the database.

So I searched online and found out that in PostgreSQL 13 there is a new DROP DATABASE "db" WITH (FORCE) syntax.

https://www.postgresql.org/docs/current/sql-dropdatabase.html

Is this something that can be added? The PR is not fully done as I need some advice on how to do this properly 🙏

[josevalim]

Should we simply call this option --force? We also need to change mix ecto.drop to make sure it accepts the --force option. Or are you actually setting this in your repo configuration? 🤔

[ruudk]

I was setting it in the Repo config but it's up for debate. I think it makes more sense as param on mix ecto.drop. Will fix.

[ruudk]

There is already a --force option on mix ecto.drop:

    * `-f`, `--force` - do not ask for confirmation when dropping the database.
      Configuration is asked only when `:start_permanent` is set to true
      (typically in production)

What do to?

[josevalim]

@ruudk I think we can reuse the option but I am not sure. What do you think @wojtekmach?

[wojtekmach]

I assume WITH FORCE is only available on pg 13+ which means it's gonna fail on earlier versions? If so, we need to add another option to not break existing users.

Let's add a --force-drop option to mix ecto.drop and perhaps say that it's only used by adapters supporting it.

[josevalim]

Maybe we can write this logic conditionally in Postgres itself, using a single command? Otherwise I would have a separate flag as I would like to avoid doing multiple operations.

[ruudk]

I tried this:

               DO $$
               DECLARE pg_version int := current_setting('server_version_num');
               BEGIN
                 IF pg_version >= 130000 THEN
                   DROP DATABASE "#{database}" WITH (FORCE);
                 ELSE
                   DROP DATABASE "#{database}";
                 END IF;
               END $$ LANGUAGE plpgsql;

But it doesn't work because you cannot drop a database inside a transaction.

ERROR 25001 (active_sql_transaction) DROP DATABASE cannot be executed from a function

[josevalim]

Yeah, so a separate flag, like --force-drop as you originally proposed is def. the best way to go IMO.

[ruudk]

I updated the PR to use force_drop from opts but it turns out that those opts are the repo.config. See https://github.com/elixir-ecto/ecto/blob/e58209ce7af4008d9015c3ff7084a20239103fbd/lib/mix/tasks/ecto.drop.ex#L74

How to proceed?

[ruudk]

Would this be Ok?

case repo.__adapter__.storage_down(Keyword.merge([force_drop: opts[:force_drop]], repo.config)) do

That would even allow you to set this up in repo.config :)

[josevalim]

💚 💙 💜 💛 ❤️

[ruudk]

Yeey, thanks for merging. How are we going to implement this on the other side? Is the repo config the way to go? Should I make a PR?

[josevalim]

Yup, what you proposed for the other side is good. :)