Investigate Export GeoPackage memory usage

[emxsys]

Investigate what appears to be excess memory consumption when exporting a GeoPackage via WPS.

[emxsys]

The large memory usage appears to be the result of internal caching by GeoServer. Heap dumps show an accumulation of byte[] arrays that are referenced by SoftReference objects. They appear to be released in occasional major garbage collections.

I compared two versions of the GeoPackage export routines, one using additional WebMap.dispose and RasterCleaner.addImage calls and the other without. Heap dumps from both were relatively identical with regards to the number and size of the byte[] objects.

[emxsys]

However, the number of surviving generation continues to climb during successive GeoPackage exports:

[emxsys]

Comparing heap dumps taken before and after a large GeoPackage export shows an accumulation of SoftReference entries:

Although the SoftReference referent values are eventually set to NULL, the queue size continues to grow and the overhead of the GC appears to rise.

[emxsys]

The org.geoserver.jai.ConcurrentTileFactory may be the owner of the SoftReference nodes.

TODO: Investigate GeoServer Image Processing and Raster Access settings.

[emxsys]

I disabled the logic used in issue #4 (CustomRenderedImageMapOutputFormat and MapResponseOutputStreamAdaptor) to see if the intermediate BufferedImage had an impact, but the results were the same.

[emxsys]

I'm ceasing the investigation for now to pursue higher priority tasks.