[postgis-devel] Parallel Support

[Even Rouault]

Le mardi 29 mars 2016 20:43:41, Paul Ramsey a écrit :
> PostgreSQL specifically doesn't do threading, it fires up background
> workers on the fly.
> The main thing we get from PostgreSQL is functionality "for free".
> Free sequence parallel, free join parallel, etc.
> If we start threading we bang up against platform differences a little
> harder than usual. I have a threading mode in the kmeans clustering,
> but it's pthreads, which makes windows compilation problematic. We
> could pull in an abstraction layer *as well*,

There's GDAL's abstraction, C callable, that could be used ( in 
cpl_multiproc.h ). If you don't want to depend on GDAL just for that, you 
could probably just borrow what is needed from port/cpl_multiproc.cpp

> but then... also the
> question of how many threads to use is a bit open, though I guess now
> we could just lean on the max_parallel_workers GUC to get the base
> database configuration info for that.
> Basically we haven't done threads on our side for historical reasons
> of portability and complexity. Times have changed though, so maybe
> it's a safer bet now.
> 
> P.
> 
> On Tue, Mar 29, 2016 at 9:44 AM, Sandro Santilli <strk at keybit.net> wrote:
> > On Tue, Mar 29, 2016 at 08:46:20AM -0700, Paul Ramsey wrote:
> >> The best suggestion so far has been from Staphen Frost, to allow the
> >> workers to run their own "finalfn" or a "worker-side combine" as I
> >> call it, so that we can cascade the sets first at the worker level,
> >> then run one final combine on master before returning.
> > 
> > How about handling threads directly from within postgis
> > or in the CascadedUnion case directly from within libgeos ?
> > 
> > What do PostgreSQL threads add to custom threads ?
> > 
> > --strk;
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