[Qgis-user] qgis multi-core processing?

[Alister Hood]

> Date: Wed, 22 Jun 2011 20:01:36 +0800
> From: maning sambale <emmanuel.sambale at gmail.com>
> Subject: Re: [Qgis-user] qgis multi-core processing?
> To: Alexander Bruy <alexander.bruy at gmail.com>
> Cc: qgis-user <qgis-user at lists.osgeo.org>
> Message-ID: <BANLkTikUGs5dWjpMq7cDZwrGqf=fC0TWrA at mail.gmail.com>
> Content-Type: text/plain; charset=UTF-8
> 
> Any reason why it wasn't added in the new release?  Many new machines
> now have multi-core, more juice we can use for computing intensive
> processes.

It _is_ planned to merge threading support into trunk, it just keeps
getting delayed.  I imagine this is partly because Martin Dobias is the
only one intending to do it, and nobody is paying him for it, so he'll
be doing it in his spare time.
Martin implied that he was busy until the end of June... so I guess we
won't be seeing anything happening before then.
 
> On Wed, Jun 22, 2011 at 7:23 PM, Alexander Bruy
> <alexander.bruy at gmail.com> wrote:
> > There is a threading-branch which introduced trhreading
> > support in QGIS. Unfortunatelly it is outdated (builded on
> > top of the QGIS 1.5)

Actually, I don't think the threading-branch really relates to "data
processing like gdal_contour generation"; it is about achieving faster
_rendering_ in QGIS.

> > 2011/6/22 maning sambale <emmanuel.sambale at gmail.com>:
> >> Just a simple question can QGIS maximize the use of multi-core for
> >> very large data procesing like gdal_contour generation?

Since QGIS tends to use command-line tools for data processing tasks
like this, I think there are two issues:
1) whether these tools support multithreading.  I'm not sure to what
extent the other gdal/ogr tools support multithreading (I seem to recall
that at least some of them do), but gdalwarp has the -multi option to
enable it, and there is a checkbox for this option in the QGIS gui.
2) whether there may be situations where the underlying tool doesn't
support multithreading, but the QGIS frontend could call more than one
instance of the tool in parallel.  If you needed to do a huge amount
with gdal_contour, maybe you could experiment to see if you can do it
faster by e.g. running two instances in parallel, both generating 10m
interval contours, but one starting at 0m, and one at 5m, then joining
the output files together.

Regards,
Alister