Re: Yet another fast GiST build

Hello Yuri,

PDEP is indeed first thing that comes up when you start googling
z-curve and bit interleaving :)
We had the code with z-curve generating PDEP instruction in PostGIS,
and dropped it since. In sorting, we now utilize sort support / prefix
search, and key generated as Hilbert curve, with fine tuning it for
different projections' geometric properties.

From this patch the most valuable thing for us is the sorting build
infrastructure itself. Maybe to get it a bit more understandable for
people not deep in geometry it makes sense to first expose the
btree_gist datatypes to this thing? So that btree_gist index on
integer will be built exactly the same way the btree index on integer
is built. This will also get everyone a reference point on the
bottlenecks and optimality of patch.

On Fri, Apr 3, 2020 at 10:56 AM Yuri Astrakhan <yuriastrakhan@gmail.com> wrote:
>
> Awesome addition!  Would it make sense to use x86's BMI2's PDEP instruction, or is the interleave computation too
smallof a percentage to introduce not-so-easy-to-port code?  Also, I think it needs a bit more documentation to explain
thelogic, i.e. a link to https://stackoverflow.com/questions/39490345/interleave-bits-efficiently ?  Thx for making it
faster:) 



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Darafei Praliaskouski
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