Race condition may lead to an incorrect count in MigrationHelpers#update_column_in_batches
This occurred in gitlab-com/operations#355 today. What can happen:
- SELECT COUNT(*) AS count FROM projects is run
totalis set to N
- A new project is created
- The update happens for all the other projects
The new project isn't marked with the default value. If
change_column_null attempts to run, it will fail, leading to a failed migration.