[postgis-devel] GiST Sorting

[Paul Ramsey]

Nevermind, I found the secret incantation:

alter operator family gist_geometry_ops_2d using gist drop function 11 (geometry);

alter operator family gist_geometry_ops_2d using gist add function 11 (geometry) geometry_gist_sortsupport_2d (internal);

P.

> On Dec 2, 2021, at 12:57 PM, Paul Ramsey <pramsey at cleverelephant.ca> wrote:
> 
> Ding ding!
> I can strip the sort support function out of the default opclass, but
> we don't have any way to add it back in, except with a direct
> alteration of the system tables. If we're OK with that, I will figure
> out the magic SQL incantation so we can document it, and strip the
> sort support function from the opclass.
> 
> P
> 
> On Wed, Dec 1, 2021 at 1:10 PM Paul Ramsey <pramsey at cleverelephant.ca> wrote:
>> 
>> So about this plan, I don't see the ALTER OPERATOR CLASS recipe that can do the thing we want.
>> 
>> https://www.postgresql.org/docs/14/sql-alteropclass.html
>> 
>> What's the magic incantation?
>> 
>>> On Dec 1, 2021, at 8:30 AM, Regina Obe <lr at pcorp.us> wrote:
>>> 
>>>> Initially there was a patch in patchset making user specify sorting function
>>>> during CREATE INDEX ON table USING gist(column) WITH
>>>> (sortfunction=zcurve). But everyone said that it's unnessecary complication and
>>>> we just made the function part of the opclass.
>>>> But sorting build was not meant to be default!
>>>> 
>>>> I'm going to work on this in December, so let's figure out what exactly do we
>>>> want from PostgreSQL 15?
>>>> 
>>>> I'm planning to work on:
>>>> 1. Fix the concurrency problem in IndexOnlyScan that Peter G. pointed out [0]
>>>> This will further slow down GiST queries a little, sorry.
>>>> 2. Sorting items within leaf page in tid order, not provided sorting function.
>>>> 3. Make better splits of leaf pages. Currently we choose how to split leaf pages
>>>> solely by sorting function. I want to use split function too. This will consume
>>>> slightly more memory, but will build better index.
>>>> 
>>>> Do we need some functionality to easily enable\disable sorting build? I think
>>>> chances are very high that we can make it better. But it still will be neither
>>>> perfect, nor better than buffered build.
>>>> 
>>>> Thanks!
>>>> 
>>>> Best regards, Andrey Borodin.
>>> [Regina Obe]
>>> I don't think I was in this discussion about CREATE INDEX ON table USING gist(column) WITH
>>>> (sortfunction=zcurve).
>>> 
>>> What was the unnecessary complication?  Was it deemed "user-facing" too complicated
>>> or "under the hood" too complicated.
>>> 
>>> For user-facing I don't see it as too complicated.  Granted it is a bit extra.
>>> But if it is deemed always not the absolute best, I feel a configure option is fine.
>>> It's only giving users redundant equally good options that I would consider too complicated.
>>> 
>>> 
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>>