Add a synchronization point after recreating missing index files to
ensure all uploads are settled and committed to the database before
the backup process continues. This prevents a race condition where
the backup could start while index files are still being uploaded.
In this case, it would be possible for the backup to reference the file that is currently being deleted. This would be very rare in production as the delays have to align and the new data must be changed and processed very quickly to trigger the issue.
In unittests we have observed the issue for a while but only showing up very rarely.
Kenneth Skovhede
ab29642e10