Generating overviews fail under specific conditions

[rprinceley]

Under specific conditions - Windows 2008R2 x64 (32bit binaries) with a specific NAS, building pyramids fail for small images. This looks like a hardware / environment specific bug and is difficult to recreate.

I tracked down the root cause to OVR not being flushed to disk in between overviews when building pyramids.

Since GDALRegenerateOverviewsMultiBand does not actually flush data to disk (TIFFFlush):

- If the compressed overview is small enough to fit in OS / file cache, 
  it does not get flushed to disk automatically.
- Next TIFF directory offset is computed based on file size which has not 
  been updated yet (because file buffers haven't been flushed).

I've added calls to GDALDataset::FlushCache() to explicitly flush OVR to disk (r22936) in 1.8-esri branch.

[Jukka Rahkonen]

Would there be a reason to do the same than in r22936 also in non-esri branch?

[Even Rouault]

This ticket has been automatically closed because Trac is no longer used for GDAL bug tracking, since the project has migrated to GitHub. If you believe this ticket is still valid, you may file it to ​https://github.com/OSGeo/gdal/issues if it is not already reported there.