I've been working with Oracle employees to find better GC tuning options. The results are good enough to share with the community:
https://wiki.apache.org/solr/ShawnHeisey#GC_Tuning With the latest Java 7 or Java 8 version, and a couple of tuning options, G1GC has grown up enough to be a viable choice. Two of the settings on that list were critical for making the performance acceptable with my testing: ParallelRefProcEnabled and G1HeapRegionSize. I've included some notes on the wiki about how you can size the G1 heap regions appropriately for your own index. Thanks, Shawn
