[postgis-users] ST_ClusterDBSCAN: is it deterministic?

[Giuseppe Broccolo]

Hi Darafei,

Thank you for your answer!

Il giorno ven 22 gen 2021 alle ore 16:26 Darafei "Komяpa" Praliaskouski <
me at komzpa.net> ha scritto:

> Hello,
>
> Cluster functions don't have cross-PostGIS-version stability guarantee.
> For many production applications that is equal to being non-deterministic.
>
> While debugging KMeans I believe I've seen blinking tests on different
> compiler flags as some optimizations may mean your distance computation
> will get different last bits and that may affect clustering, especially on
> grids.
>

I see the problem here. In my company we use the DBSCAN algorithm to
cluster some geometries and we are experiencing the not deterministic
behaviour, even running on the same datasets. Since the geometries are
included on a specific window partition we define in the query, I was
curious to know if there was any trick in order to have reproducible
results considering exactly the same boundary conditions - same underlying
architecture, same PostgreSQL version, of course same input. But I see it's
a bit pretentious :)

Thanks again,
Giuseppe.
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