1 files changed, 18 insertions, 6 deletions
diff --git a/spec/support/database/prevent_cross_database_modification.rb b/spec/support/database/prevent_cross_database_modification.rb
index b4c968e3c41..7ded85b65ce 100644
--- a/spec/support/database/prevent_cross_database_modification.rb
+++ b/spec/support/database/prevent_cross_database_modification.rb
@@ -33,8 +33,10 @@ module Database
       end
 
       def cleanup_with_cross_database_modification_prevented
-        ActiveSupport::Notifications.unsubscribe(PreventCrossDatabaseModification.cross_database_context[:subscriber])
-        PreventCrossDatabaseModification.cross_database_context[:enabled] = false
+        if PreventCrossDatabaseModification.cross_database_context
+          ActiveSupport::Notifications.unsubscribe(PreventCrossDatabaseModification.cross_database_context[:subscriber])
+          PreventCrossDatabaseModification.cross_database_context[:enabled] = false
+        end
       end
     end
 
@@ -55,8 +57,11 @@ module Database
     end
 
     def self.prevent_cross_database_modification!(connection, sql)
+      return unless cross_database_context
       return unless cross_database_context[:enabled]
 
+      return if connection.pool.instance_of?(ActiveRecord::ConnectionAdapters::NullPool)
+
       database = connection.pool.db_config.name
 
       if sql.start_with?('SAVEPOINT')
@@ -74,6 +79,8 @@ module Database
 
       return if cross_database_context[:transaction_depth_by_db].values.all?(&:zero?)
 
+      # PgQuery might fail in some cases due to limited nesting:
+      # https://github.com/pganalyze/pg_query/issues/209
       parsed_query = PgQuery.parse(sql)
       tables = sql.downcase.include?(' for update') ? parsed_query.tables : parsed_query.dml_tables
 
@@ -87,7 +94,8 @@ module Database
       if schemas.many?
         raise Database::PreventCrossDatabaseModification::CrossDatabaseModificationAcrossUnsupportedTablesError,
           "Cross-database data modification of '#{schemas.to_a.join(", ")}' were detected within " \
-          "a transaction modifying the '#{all_tables.to_a.join(", ")}'"
+          "a transaction modifying the '#{all_tables.to_a.join(", ")}' tables." \
+          "Please refer to https://docs.gitlab.com/ee/development/database/multiple_databases.html#removing-cross-database-transactions for details on how to resolve this exception."
       end
     end
   end
@@ -96,16 +104,20 @@ end
 Gitlab::Database.singleton_class.prepend(
   Database::PreventCrossDatabaseModification::GitlabDatabaseMixin)
 
+CROSS_DB_MODIFICATION_ALLOW_LIST = Set.new(YAML.load_file(File.join(__dir__, 'cross-database-modification-allowlist.yml'))).freeze
+
 RSpec.configure do |config|
   config.include(::Database::PreventCrossDatabaseModification::SpecHelpers)
 
   # Using before and after blocks because the around block causes problems with the let_it_be
   # record creations. It makes an extra savepoint which breaks the transaction count logic.
-  config.before(:each, :prevent_cross_database_modification) do
-    with_cross_database_modification_prevented
+  config.before do |example_file|
+    if CROSS_DB_MODIFICATION_ALLOW_LIST.exclude?(example_file.file_path)
+      with_cross_database_modification_prevented
+    end
   end
 
-  config.after(:each, :prevent_cross_database_modification) do
+  config.after do |example_file|
     cleanup_with_cross_database_modification_prevented
   end
 end