Re: maintenance memory vs autovac

Tom Lane wrote:
> Magnus Hagander <magnus@hagander.net> writes:
>> Greg Stark wrote:
>>> One concern I have about this is people asking "how come when I
>>> runvacuum manually it takes x minutes but when autovacuum runs it it
>>> tale 5x minutes?"
> 
>> As long as the default is the same, people would get at least an initial
>> clue that it might have something to do with them changing a
>> configuration parameter...
> 
> It seems like mostly a confusion-generator to me.  Is there any actual
> evidence that autovac should use a different maintenance_work_mem than
> other processes?

The use-case that made me think of that is one with lots of autovac
workers in a system with lots of small tables in different databases.

Turns out I read the documentation for autovac wrong. I understood that
if I wanted it to look at 1000 databases at once, I needed
autovac_workers at 1000. Talked a bit offlist with Alvaro and realized
that's not what it is, but that the documentation is a bit unclear on
that - will work on fixing that.

Which means there's probably no real use-case for "lots of autovac
workers that each needs only a little maint_work_mem", in which case
having such an extra parameter would become unnecessary.

//Magnus