Inspired by multiple Solr mailing list entries during the last month or two, I did some search performance testing on our 11M documents / 49GB index using logged queries on Solr 4 with MMapDirectory. It turns out that our setup with Solid State Drives and 8GB of RAM (which leaves 5GB for disk cache) performs nearly as well as having the whole index in disk cache; the SSD solution delivering ~425 q/s for non-faceted searches and the memory solution delivering ~475 q/s (roughly estimated from the graphs, sorry). Going full memory cache certainly is faster if we ignore warmup, but those last queries/second are quite expensive.
http://sbdevel.wordpress.com/2013/06/06/memory-is-overrated/ Regards, Toke Eskildsen, State and University Library, Denmark
