Large tiled tiff catalogs exhibit slow performance

[trevorwekel]

MapGuide exhibits slow performance with very large tiled tiff catalogs (ie. thousands of images). Part of the performance slowdown is due to catalog parsing overhead occuring on (nearly) every request. Since the server is limited to a single raster provider connection, accessing multiple raster feature sources will cause the catalog to unload and reload for every request.

This can be reproduced by a single user with two catalogs of the same data at different pixel resolutions. Two layers should be constructed from the two data sets with adjacent scale ranges. When viewed, pans on the same layer are fast. Zoom in or zoom out across the two layers is significantly slower.

The fix is to enable multiple connections to the raster provider. With multiple connections, the catalogs will not be regenerated on every request.

[trevorwekel]

Code changes submitted to 2.0.x stream ​http://trac.osgeo.org/mapguide/changeset/3312