SOLR-1292: followup tweak based on mailing list discussion: for indexes with lots of segments, estimating the size of all the field caches can take a lot of time (particularly with lots of String based caches) so for now we only estimate the size for items which are part of instanity instances
lucene/solr/trunk/src/java/org/apache/solr/search/SolrFieldCacheMBean.java