Remove foreign key contraint in table job_warnings on 'fk_jobs_id' (#4174)

The job_warnings table was created in a wrong way. There are two columns 'job_id' and 'fk_jobs_id'.
There is a foreign key constraint on 'fk_jobs_id', which references jobs(id).
CC coding never inserts data into 'fk_jobs_id', but only into 'job_id'.
So the foreign key constraint is not needed and causes way slower cleanup of pollable jobs,
which can even run into DB statement timeouts and cause an ever growing table.

Author: svkrieger

db/migrations/20250116144231_remove_unnecessary_fk_in_job_warnings.rb

@@ -0,0 +1,9 @@
+Sequel.migration do
+  up do
+    unless foreign_key_list(:job_warnings).empty?
+      alter_table :job_warnings do
+        drop_foreign_key :fk_jobs_id
+      end
+    end
+  end
+end

spec/migrations/20250116144231_remove_unnecessary_fk_in_job_warnings_spec.rb

@@ -0,0 +1,31 @@
+require 'spec_helper'
+require 'migrations/helpers/migration_shared_context'
+
+RSpec.describe "migration to remove foreign key constraint on table 'job_warnings' and column 'fk_jobs_id'", isolation: :truncation, type: :migration do
+  include_context 'migration' do
+    let(:migration_filename) { '20250116144231_remove_unnecessary_fk_in_job_warnings.rb' }
+  end
+
+  describe 'job_warnings table' do
+    it 'removes the fk constraint as well as the column' do
+      Sequel::Migrator.run(db, migrations_path, target: current_migration_index, allow_missing_migration_files: true)
+
+      expect(db.foreign_key_list(:job_warnings)).to be_empty
+      expect(db[:job_warnings].columns).not_to include(:fk_jobs_id)
+    end
+
+    context 'foreign key constraint does not exist' do
+      before do
+        unless db.foreign_key_list(:job_warnings).empty?
+          db.alter_table(:job_warnings) do
+            drop_foreign_key :fk_jobs_id
+          end
+        end
+      end
+
+      it 'does not fail' do
+        expect { Sequel::Migrator.run(db, migrations_path, target: current_migration_index, allow_missing_migration_files: true) }.not_to raise_error
+      end
+    end
+  end
+end