All tables are truncated when using tests in parallel.

[cduez]

I was wondering why rails was truncating all the tables only when the tests are executed in parallel using the :fork strategy and not with the :thread strategy?

I have noticed this after creating a new rails application with an already existing database: My first test was already taking seconds to run which didn't seem right. The test log showed that before the first test is executed, all the tables are truncated which take few seconds in my case.

When a fork is created rails calls the method:

rails/activerecord/lib/active_record/tasks/database_tasks.rb

Line 350 in 4fbb393

def reconstruct_from_schema(db_config, format = ActiveRecord::Base.schema_format, file = nil) # :nodoc:

which truncates the tables if there is no change in the schema:

if schema_up_to_date?(db_config, format, file)
  truncate_tables(db_config)
else
  purge(db_config)
  load_schema(db_config, format, file)
end

Would it be acceptable to do nothing if the schema is up to date in order to save some time?

System configuration

Rails version: 6.0.2.1

Ruby version: 2.6.5

[rails-bot]

This issue has been automatically marked as stale because it has not been commented on for at least three months.
The resources of the Rails team are limited, and so we are asking for your help.
If you can still reproduce this error on the 6-0-stable branch or on master, please reply with all of the information you have about it in order to keep the issue open.
Thank you for all your contributions.

[joegaudet]

I'm seeing the same issue, which wouldn't normally be a problem but it's nuking my PostGIS constants.

[brendon]

Yes this caught me too. I was seeding my test database and this just wiped it again before the tests ran.

[feliperaul]

This caught me as well. How are we supposed to seed the test database when using parallel tests?

[joegaudet]

The issue was the postgis plugin.

…

On Mon, Oct 25, 2021 at 11:49 AM flprben ***@***.***> wrote: This caught me as well. How are we supposed to seed the test database when using parallel tests? — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#38164 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAA6IB65XYKRCPIQL6UENU3UIWRB7ANCNFSM4KDF6JYA> .

[malomalo]

Anyone figure this out? Truncating all the tables in the database truncates spatial_ref_sys which breaks PostGIS. I don't see a way to ignore certain table either.

[malomalo]

Ah for anyone else who runs into this PostGIS adapter has its own truncate_tables which hides the table from Rails. Currently no way to ignore certain tables for test, so best to monkey patch truncate_tables on your adapter

[cduez]

An environment variable was added which skips the table truncation and mitigates this issue, see #51686

[malomalo]

@cduez that works if all the tables don't need truncating and getting all the devs to set the variable. But that seem more just like a CI solution.

A better solution would be a config setting. But for now patching the connection adapter ala Postgis Adapter works better