RE: A failure in t/038_save_logical_slots_shutdown.pl

Dear Amit, Bharath,

> This is a more strict check because it is possible that even if the
> latest confirmed_flush location is not persisted there is no
> meaningful decodable WAL between whatever the last confirmed_flush
> location saved on disk and the shutdown_checkpoint record.
> Kuroda-San/Vignesh, do you have any suggestion on this one?

I think it should be as testcase explicitly. There are two reasons:
 
* e0b2eed is a commit for backend codes, so it should be tested by src/test/*
  files. Each src/bin/XXX/*.pl files should test only their executable.
* Assuming that the feature would be broken. In this case 003_logical_slots.pl
  would fail, but we do not have a way to recognize on the build farm.
  038_save_logical_slots_shutdown.pl helps to distinguish the case.
 
Based on that, I think it is OK to add advance_wal() and comments, like Bharath's patch.

Best Regards,
Hayato Kuroda
FUJITSU LIMITED