[gdal-dev] RFC 47 Status.

[Even Rouault]

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/1kHOoZfnqcWCR1S3I49RWoddG2tGxCXxXkjSjANJ2Gh0/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
> 
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