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Better fix for PG::ObjectInUse error when dropping multiple databases

Thong Kuah requested to merge patch_drop_database_connections_drop_task into master

What does this MR do and why?

This requires a few things to be true:

  1. Database connections are opened during initialization. This is true for the GitLab application. Note this is not allowed anymore in Rails 7.
  2. Multiple databases are configured. With a single database, Rails has always accidentally closed the database connection for the main database.

This fix removes prior attempts to drop the connection(s) in favor of a fix closer to where the database will be dropped.

Related issue: #356656 (closed)

Reproduction

  1. Setup multiple databases following #356353 (closed)
  2. Comment out the enhancement using clear_all_connections in lib/tasks/gitlab/db.rake if in master branch`
  3. Run RAILS_ENV=test be rails db:test:prepare 
(arm64) tkgl2:gitlab tkuah$ RAILS_ENV=test be rails db:test:prepare
WARNING: sha256_attribute :fingerprint_sha256 is invalid since the table doesn't exist - you may need to run database migrations

rails aborted!
ActiveRecord::StatementInvalid: PG::ObjectInUse: ERROR:  database "gitlabhq_test_ci" is being accessed by other users
DETAIL:  There is 1 other session using the database.
/Users/tkuah/code/gdk-ee/gitlab/lib/gitlab/database/load_balancing/connection_proxy.rb:119:in `block in write_using_load_balancer'
/Users/tkuah/code/gdk-ee/gitlab/lib/gitlab/database/load_balancing/load_balancer.rb:112:in `block in read_write'
/Users/tkuah/code/gdk-ee/gitlab/lib/gitlab/database/load_balancing/load_balancer.rb:172:in `retry_with_backoff'
/Users/tkuah/code/gdk-ee/gitlab/lib/gitlab/database/load_balancing/load_balancer.rb:110:in `read_write'
/Users/tkuah/code/gdk-ee/gitlab/lib/gitlab/database/load_balancing/connection_proxy.rb:118:in `write_using_load_balancer'
/Users/tkuah/code/gdk-ee/gitlab/lib/gitlab/database/load_balancing/connection_proxy.rb:88:in `method_missing'

Caused by:
PG::ObjectInUse: ERROR:  database "gitlabhq_test_ci" is being accessed by other users
DETAIL:  There is 1 other session using the database.
/Users/tkuah/code/gdk-ee/gitlab/lib/gitlab/database/load_balancing/connection_proxy.rb:119:in `block in write_using_load_balancer'
/Users/tkuah/code/gdk-ee/gitlab/lib/gitlab/database/load_balancing/load_balancer.rb:112:in `block in read_write'
/Users/tkuah/code/gdk-ee/gitlab/lib/gitlab/database/load_balancing/load_balancer.rb:172:in `retry_with_backoff'
/Users/tkuah/code/gdk-ee/gitlab/lib/gitlab/database/load_balancing/load_balancer.rb:110:in `read_write'
/Users/tkuah/code/gdk-ee/gitlab/lib/gitlab/database/load_balancing/connection_proxy.rb:118:in `write_using_load_balancer'
/Users/tkuah/code/gdk-ee/gitlab/lib/gitlab/database/load_balancing/connection_proxy.rb:88:in `method_missing'
Tasks: TOP => db:test:load => db:test:purge
(See full trace by running task with --trace)

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Edited by Thong Kuah

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