Re: We probably need autovacuum_max_wraparound_workers

Robert Haas <robertmhaas@gmail.com> writes:
> For example, suppose that 26 tables each of which is 4GB in size are
> going to simultaneously come due for an anti-wraparound vacuum in 26
> hours.  For the sake of simplicity suppose that each will take 1 hour
> to vacuum.  What we currently do is wait for 26 hours and then start
> vacuuming them all at top speed, thrashing the I/O system.

This is a nice description of a problem that has nothing to do with
reality.  In the first place, we don't vacuum them all at once; we can
only vacuum max_workers of them at a time.  In the second place, the
cost-delay features ought to be keeping autovacuum from thrashing the
I/O, entirely independently of what the reason was for starting the
vacuums.  Clearly, since people are complaining, there's something that
needs work there.  But not the work you're proposing.
        regards, tom lane