Hi,
On 2019-02-18 19:01:06 -0500, Tom Lane wrote:
> Andres Freund <andres@anarazel.de> writes:
> > Isn't a large portion of benefits in this patch going to be mooted by
> > the locking improvements discussed in the other threads? I.e. there's
> > hopefully not going to be a ton of cases with low overhead where we
> > acquire a lot of locks and release them very soon after. Sure, for DDL
> > etc we will, but I can't see this mattering from a performance POV?
>
> Mmm ... AIUI, the patches currently proposed can only help for what
> David called "point lookup" queries. There are still going to be
> queries that scan a large proportion of a partition tree, so if you've
> got tons of partitions, you'll be concerned about this sort of thing.
Agreed - but it seems not unlikely that for those the rest of the
planner / executor overhead will entirely swamp any improvement we could
make here. If I understand correctly the benchmarks here were made with
"point" update and select queries, although the reference in the first
post in this thread is a bit vague.
> > I'm not against doing something like Tom proposes, but heuristics with
> > magic constants like this tend to age purely / are hard to tune well
> > across systems.
>
> I didn't say it had to be a constant ...
Do you have good idea?
Greetings,
Andres Freund