[Qgis-developer] Possible memory leak in QGIS redraws?

Nyall Dawson nyall.dawson at gmail.com
Wed Oct 21 00:49:44 PDT 2015

On 21 Oct 2015 3:20 PM, "Nyall Dawson" <nyall.dawson at gmail.com> wrote:
> On 9 October 2015 at 01:45, RĂ©gis Haubourg
> <regis.haubourg at eau-adour-garonne.fr> wrote:
> > Hi all,
> > I try to narrow down a production issue here.
> > In long sessions with lot's of redraws on complex projects, memory
seems to
> > increase regularly.
> >
> > In a more simple environnement with no plugins, just sending multiple
> > redraws using F5 key triggers it.
> > It grows quite fast on 2.6 up to 4Go sometimes, quite slower in master
> > 2.10. Every 5-6 redraws, QGIS adds 1Mo of RAM in 2.6, less often in
> > versions.
> >
> > If confirmed, and if nothing else is to be blamed (windows?, QT?) this
is a
> > serious issue for enterprise uses, especially if we want to build
> > application that run all day long with many canvas redraws.
> >
> I've done some more testing, using valgrind and massif. Here's what I've
> - there's a big leak coming from Qt's font database. Fixed in Qt 5.1
> (https://bugreports.qt.io/browse/QTBUG-26861). About 50% of the memory
> leaked is caused by this one. We could possibly work around it by
> having a singleton so we only ever use one QFontDatabase in QGIS, or
> just get on with the move to Qt5 and get the proper fix for free. ;)
> - I also see a lot of memory used by Python objects. Specifically, a
> lot coming from QgsPythonUtilsImpl::evalString and the PyRun_String
> call in that function. I don't think these are leaks though (at least,
> not within QGIS). But that's the second largest memory allocator I see
> reported by massif
> - There was a small leak of a GEOS object in labeling... don't think
> this would cause too much memory usage though. I'll submit a fix after
> giving it some more testing.
> - Lastly, the remaining large chunk of allocated memory is used by the
> images stored during rendering. I'm 90% sure these are all properly
> cleaned, but I still can't throw the niggling suspicion that just
> maybe there's some special condition in which these images aren't
> properly deleted.
> So yeah... no magic fixes to this one unfortunately. (At least, not
> until QGIS 3.0!)

Actually... Scratch that. Just found some huge leaks in certain
circumstances. Fixes in progress.


> Nyall
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