Re: Overhauling GUCS

Gregory Stark wrote:
>
> I think we do a pretty good job of this already. Witness things like
> effective_cache_size -- imagine if this were "nested_loop_cache_hit_rate" for
> example, good luck figuring out what to set it to.

I think either of these are fine if we describe how to measure
them. Ideally if we had a GUC that said "log_nested_loop_cache_hit_rate"
that enabled some timing code (understandably with lots of overhead) that
made an attempt to measure the hit rate, it'd be easier to figure out
than the effective cache size, no?

> The vacuum cost delay factors are probably ripe for such a recast though. I
> think we need just one parameter "vacuum_io_bandwidth" or something like that.

+1; though perhaps the inverse of that is more useful. When my
machines are idle I'd be happy if they vacuum more. Wouldn't
we be better served specifying the I/O bandwidth of each device/tablespace
and letting vacuum use whatever portion would be otherwise idle?

> The bgwriter parameters might also be a candidate but I'm less certain.