[gdal-dev] MBTiles creation problems on some iOS devices

[gunnarblom]

Hi.

I'm using GDALTranslate() in C++ to convert GTiffs (5k*5k pixels) to MBTiles
(resulting size: ~60mb) on iOS.

It works good on iPhone 6 (1GB ram), iPhone 6S (2GB ram, peaks GDAL usage at
160mb) and iPad Mini 3 (1GB ram) and takes around 1-3 minutes. But on e.g.
iPhone 5S (1GB ram), iPad 3 (1GB ram) and iPad 4 (1GB ram), it takes forever
(never succeeded with it so far, takes too long).

What is happening is that on the older devices, GDAL starts to write a lot
to the disk for some reason. It starts normally and with CPU at 100% for a
while. Then the writing to disk starts and the CPU goes up and down a lot
but never at consistent high levels. When I stopped it at 50% progress, it
had written ~5GB to disk. The iPhone 6S writes  less than 100MB and keeps
CPU at 100% all the way. All devices have a couple of hundred MB free ram
during the whole process.

If I add GDALSetCacheMax(1000 * 1024 * 1024) before converting on iPad 3, it
succeeds but after a long time and still writes ~1GB of data that slows the
process a lot (and peaks GDAL memory usage at 250mb, compared to iPhone 6S
that peaks at 160mb GDAL ram usage).

1) What might be wrong here? What situation triggers GDAL to write so much
to disk even if the RAM seems at good free levels?
2) I can set the disk cache with GDALSetCacheMax, any way to set the other
memory used by this function? (memory for the actual conversion)


Br,
Gunnar Blom



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