[gdal-dev] RFC 47 Status.

[Tomaka, Jacek]

>I was wondering why you mention 125 ms, but a grep shows that there's such a delay in the Windows implementation of CPLAcquireMutex() when the critical section fails to be acquired, so I guess you >must think to that ?

Yes. I would not have come up with such a number myself ;) It is not prime ;) 

>Well, the tests in my slides have only be done on Linux where there's no such sleep (just rely on pthread implementation).

That is not a good news for Windows. But I will test it... 

Regards.
Jacek Tomaka

-----Original Message-----
From: Even Rouault [mailto:even.rouault at spatialys.com] 
Sent: Thursday, 7 May 2015 9:20 PM
To: Tomaka, Jacek
Cc: gdal-dev at lists.osgeo.org
Subject: Re: [gdal-dev] RFC 47 Status.

Le jeudi 07 mai 2015 15:13:51, Tomaka, Jacek a écrit :
> Even,
> 
> That makes sense to me.
> I will try to test your mutexing changes to see if it improves our use 
> cases. Maybe your locking improvements will solve all the problems we 
> are seeing. Out of curiosity, the second value test on the slide, was 
> it with sleep of 125 ms in case of contention?

I was wondering why you mention 125 ms, but a grep shows that there's such a delay in the Windows implementation of CPLAcquireMutex() when the critical section fails to be acquired, so I guess you must think to that ?
Well, the tests in my slides have only be done on Linux where there's no such sleep (just rely on pthread implementation).

> 
> Regards.
> Jacek Tomaka
> 
> 
> -----Original Message-----
> From: Even Rouault [mailto:even.rouault at spatialys.com]
> Sent: Thursday, 7 May 2015 8:45 PM
> To: Tomaka, Jacek
> Cc: gdal-dev at lists.osgeo.org
> Subject: Re: [gdal-dev] RFC 47 Status.
> 
> Le jeudi 07 mai 2015 14:20:42, Tomaka, Jacek a écrit :
> > Even,
> > 
> > I am not sure I understand what you are saying about 2.0 beta. Does it
> > mean that it is too late for inclusion or it did not make it to the
> > beta but can still make it to 2.0?
> 
> Now that we are in beta, I wouldn't normally expect new RFCs to be
> implemented for 2.0 final that are not already in the beta.
> 
> > Given that the functionality is enabled by setting
> > GDAL_DATASET_CACHING=YES it should not be too destabilizing?
> 
> It still implies changing core classes. Anyway, the implementation isn't
> ready enough (2 different implementations, no tests etc...) and the RFC
> not finalized to expose the final solution. Somehow, for me, it goes a bit
> too far currently and should be rectricted only on adding the possibility
> of a per-dataset block cache. Further work on multithreaded access to a
> same dataset should be the subject of another RFC.
> 
> > I agree that per-dataset block cache is huge improvement. Especially
> > in scenarios when different threads are reading different files/datasets.
> > 
> > If there is chance for it to still be included in 2.0 please let me
> > know what needs to be done to make it happen.
> 
> Well, someone would need to champion it & very quickly. But I don't see a
> compelling reason to absolutely put it in GDAL 2.0. I'd note I've done
> subtle improvements related to the scope of the mutex of the block cache
> (e.g. no longer making it a recursive mutex, but a regular one) during the
> 2.0 cycle that already reduce lock contention in some use cases (see slide
> 39 of
> https://docs.google.com/presentation/d/1kHOoZfnqcWCR1S3I49RWoddG2tGxCXxXkj
> SjANJ2Gh0/pub?start=false&loop=false&delayms=3000#slide=id.g7b40ab322_227
> ). Further work like RFC 47 could go into 2.1
> 
> As far as I'm concerned, I'll revisit in the coming weeks (for 2.1) another
> older RFC in the same area of raster blocks
> (https://trac.osgeo.org/gdal/wiki/rfc26_blockcache, to deal with WMS/WMTS
> datasets that have dimensions nearing 1 billion x 1 billion pixels and
> thus a huge block address space), but that's a bit orthogonal to the
> per-dataset vs global block cache.
> 
> Even
> 
> > Regards.
> > Jacek Tomaka
> > 
> > -----Original Message-----
> > From: Even Rouault [mailto:even.rouault at spatialys.com]
> > Sent: Thursday, 7 May 2015 8:05 PM
> > To: gdal-dev at lists.osgeo.org
> > Cc: Tomaka, Jacek
> > Subject: Re: [gdal-dev] RFC 47 Status.
> > 
> > Jacek,
> > 
> > > What is the current status of RFC 47?
> > 
> > Pending. IMHO the per-dataset block cache vs global block cache looks
> > good. I'm less convinced by the attempts to provide even limited
> > multi-threaded access to a same GDALDataset object.
> > 
> > > Is per dataset caching going to make it to GDAL 2.0?
> > 
> > No, not that we are now in beta phase.
> > 
> > Even
> > 
> > --
> > Spatialys - Geospatial professional services http://www.spatialys.com

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