RE: Introduce XID age and inactive timeout based replication slot invalidation

Dear Nisha,

Thanks for updating the patch!

> Fixed. It is reasonable to align with other timeout parameters by
> using milliseconds as the unit.

It looks you just replaced to GUC_UNIT_MS, but the documentation and
postgresql.conf.sample has not been changed yet. They should follow codes.
Anyway, here are other comments, mostly cosmetic.

01. slot.c

```
+int         replication_slot_inactive_timeout_ms = 0;
```

According to other lines, we should add a short comment for the GUC.

02. 050_invalidate_slots.pl

Do you have a reason why you use the number 050? I feel it can be 043.

03. 050_invalidate_slots.pl

Also, not sure the file name is correct. This file contains only a slot invalidation due to the
replication_slot_inactive_timeout. But I feel current name is too general.

04. 050_invalidate_slots.pl

```
+use Time::HiRes qw(usleep);
```

This line is not needed because usleep() is not used in this file.

Best regards,
Hayato Kuroda
FUJITSU LIMITED