[postgis-devel] ST_Subdivide Defaults

[Darafei "Komяpa" Praliaskouski]

You did that some years ago and ignored my note to update docs:
https://github.com/postgis/postgis/commit/feac7c6ed625bea34de847605a590abdb627bd13

пт, 21 сту 2022, 20:35 карыстальнік Paul Ramsey <pramsey at cleverelephant.ca>
напісаў:

> A user was talking about how much faster ST_Subdivide made their query,
> and their example was materializing the subdivided geometries into a table,
> building an index, and then using that downstream.
>
> Here's the thing: the default numVertices of ST_Subdivide is 256. Which
> (256 * 2 * 8 = 4096) is half of a full page, but actually kind of close to
> the TOAST threshold. At a minimum with standard storage defaults, it'll be
> getting compressed inline, if not actually TOASTed still. Which will hurt
> performance.
>
> I was thinking that a 128 or even 96 point default might make a lot more
> sense. At 128 vertices (2048 bytes) we're still flirting with inline
> compression, so maybe 96 (1536b) or even 64 vertices (1024b) would be best.
>
> In general, it seems like a missed upportunity to have something shredding
> down geometries but still be over-running the TOAST thresholds, that we
> know have performance implications, when the whole point of the shredding
> is improved performance.
>
> Thoughts?
>
> P
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