Re: WIP: BRIN multi-range indexes

Hi!

I'm starting to look at this patchset. In the general, I think it's
very cool! We definitely need this.

On Tue, Apr 3, 2018 at 10:51 PM Tomas Vondra
<tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
> 1) index parameters
>
> The main improvement of this version is an introduction of a couple of
> BRIN index parameters, next to pages_per_range and autosummarize.
>
> a) n_distinct_per_range - used to size Bloom index
> b) false_positive_rate - used to size Bloom index
> c) values_per_range - number of values in the minmax-multi summary
>
> Until now those parameters were pretty much hard-coded, this allows easy
> customization depending on the data set. There are some basic rules to
> to clamp the values (e.g. not to allow ndistinct to be less than 128 or
> more than MaxHeapTuplesPerPage * page_per_range), but that's about it.
> I'm sure we could devise more elaborate heuristics (e.g. when building
> index on an existing table, we could inspect table statistics first),
> but the patch does not do that.
>
> One disadvantage is that those parameters are per-index.

For me, the main disadvantage of this solution is that we put
opclass-specific parameters into access method. And this is generally
bad design. So, user can specify such parameter if even not using
corresponding opclass, that may cause a confuse (if even we forbid
that, it needs to be hardcoded). Also, extension opclasses can't do
the same thing. Thus, it appears that extension opclasses are not
first class citizens anymore. Have you take a look at opclass
parameters patch [1]? I think it's proper solution of this problem.
I think we should postpone this parameterization until we push opclass
parameters patch.

1. https://www.postgresql.org/message-id/d22c3a18-31c7-1879-fc11-4c1ce2f5e5af%40postgrespro.ru

------
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company