Re: Restart pg_usleep when interrupted

I'm trying to understand what the point of this patch is, so I went to 
read this thread from the beginning:

> In the proposal by Bertrand [1] to implement vacuum cost delay tracking
> in pg_stat_progress_vacuum, it was discovered that the vacuum cost delay
> ends early on the leader process of a parallel vacuum due to parallel workers > reporting progress on index
vacuuming,which was introduced in 17
 
> with commit [2]. With this patch, everytime a parallel worker
> completes a vacuum index, it will send a completion message to the leader.

Ok, so we might sometimes skip the sleep, if an interrupt is received. I 
agree that's a bit sloppy, but probably won't make any difference in 
practice.

> The facility that allows a parallel worker to report progress to the leader was
> introduced in commit [3].
>
> In the case of the patch being proposed by Bertrand, the number of interrupts > will be much more frequent as
parallelworkers would send a message 
 
to the leader
> to update the vacuum delay counters every vacuum_delay_point call.

Hmm, I wonder if that's a good design, if it results in a lot of interrupts.

On the patch itself: Making the sleeps in vacuum uninterruptible means 
that vacuum will be more slow to respond to interrupts. If you SIGTERM a 
vacuum process, or hit CTRL-C, you *would* want to exit the sleep ASAP.

Tom raised that concern earlier in this thread 
(https://www.postgresql.org/message-id/2100439.1719610468%40sss.pgh.pa.us), 
but it seems the discussion wandered off to the details of how to do the 
sleep, and left that unaddressed.

-- 
Heikki Linnakangas
Neon (https://neon.tech)