Drop and re-create the test DB when a table has too many columns

Signed-off-by: Rémy Coutable <remy@rymai.me>

spec/support/database_cleaner.rb

@@ -15,6 +15,39 @@ RSpec.configure do |config|
     delete_from_all_tables!
   end
 
+  config.append_after(:context, :migration) do
+    delete_from_all_tables!
+
+    # Postgres maximum number of columns in a table is 1600 (https://github.com/postgres/postgres/blob/de41869b64d57160f58852eab20a27f248188135/src/include/access/htup_details.h#L23-L47).
+    # And since:
+    # "The DROP COLUMN form does not physically remove the column, but simply makes
+    # it invisible to SQL operations. Subsequent insert and update operations in the
+    # table will store a null value for the column. Thus, dropping a column is quick
+    # but it will not immediately reduce the on-disk size of your table, as the space
+    # occupied by the dropped column is not reclaimed.
+    # The space will be reclaimed over time as existing rows are updated."
+    # according to https://www.postgresql.org/docs/current/sql-altertable.html.
+    # We drop and recreate the database if any table has more than 1200 columns, just to be safe.
+    max_allowed_columns = 1200
+    tables_with_more_than_allowed_columns =
+      ApplicationRecord.connection.execute("SELECT attrelid::regclass::text AS table, COUNT(*) AS column_count FROM pg_attribute GROUP BY attrelid HAVING COUNT(*) > #{max_allowed_columns}")
+
+    if tables_with_more_than_allowed_columns.any?
+      tables_with_more_than_allowed_columns.each do |result|
+        puts "The #{result['table']} has #{result['column_count']} columns."
+      end
+      puts "Recreating the database to reset the 'application_settings' columns count"
+      start = Gitlab::Metrics::System.monotonic_time
+
+      ActiveRecord::Tasks::DatabaseTasks.drop_current
+      ActiveRecord::Tasks::DatabaseTasks.create_current
+      ActiveRecord::Tasks::DatabaseTasks.load_schema_current
+      ActiveRecord::Tasks::DatabaseTasks.migrate
+
+      puts "Schema re-creation done in #{Gitlab::Metrics::System.monotonic_time - start}"
+    end
+  end
+
   config.around(:each, :delete) do |example|
     self.class.use_transactional_tests = false