I don't do Solr, but had this thought that might be interesting: instead of associating cache with an IndexSearcher, it could stand by it self. When new documents are inserted (if I understand it right, Solr have some kind of notification system for this) the cached queries are placed on the new documents (indexed in a Memory- or InstantiatedIndex [Lucene issue 550]) to see if they affect the cached results. If not, cache is kept. If, cache is rebuilt or removed. With pre-tokenized fields (Lucene issue 580) it would not consume that much resources at all, but perhaps that will not fit in the Solr-scheme.
Any immediate comments on that? I'd like to implement something like this for my self as I notice the CPU working a bit harder than I want it to every time I update an index.
