Re: Deadline-Based Vacuum Delay

Galy Lee <lee.galy@oss.ntt.co.jp> writes:
> It is true that there is not a decent way to estimate the amount of work 
> to be done. But the purpose in here is not “spread the vacuum over 6 
> hours exactly”, it is “finish vacuum within 6 hours, and spread the 
> spikes as much as possible”. So the maximum estimation of the work is 
> enough to refine the vacuum within the window, it is fine if vacuum run 
> quickly than schedule.

Is it?  If I tell the thing to take 6 hours and it finishes in 5
minutes, why would I be happy?  It could obviously have spread out the
work more, and presumably if I'm using this feature at all then I want
the least possible load added from vacuum while it's running.

But this is all academic, because there's no way to produce a
trustworthy "maximum estimate" either.
        regards, tom lane