On 10/20/21 20:33, John Naylor wrote:
On Wed, Oct 20, 2021 at 2:23 PM Tomas Vondra
<tomas.von...@enterprisedb.com <mailto:tomas.von...@enterprisedb.com>>
wrote:
>
> Couldn't we simply inspect the visibility map, use the index data only
> for fully visible/summarized ranges, and inspect the heap for the
> remaining pages? That'd still be a huge improvement for tables with most
> only a few pages modified recently, which is a pretty common case.
>
> I think the bigger issue is that people rarely do COUNT(*) on the whole
> table. There are usually other conditions and/or GROUP BY, and I'm not
> sure how would that work.
Right. My (possibly hazy) recollection is that people don't have quite
as high an expectation for queries with more complex predicates and/or
grouping. It would be interesting to see what the balance is.
I don't know where the balance is, and I doubt it's possible to answer
that in general - I'm sure some workloads might benefit significantly.
I wonder if multi-column BRIN indexes would help in cases with
additional predicates. Seems possible.
BTW you mentioned using BRIN indexes for min/max - I've been thinking
about using BRIN indexes for ordering/sorting, which seems related. And
I think it's actually doable, so I wonder why you concluded using BRIN
indexes for min/max is not possible?
regards
--
Tomas Vondra
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
