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