: is there a way (or formula) to determine the required amount of RAM memory, : e.g. by number of documents, document size?
There's a lot of factors that come into play ... number of documents and size of documents aren't nearly as significant as number of unique indexed terms. : with 4.000.000 documents, searching the index is quite fast, but when I trie : to sort the results, I get the well-known OutOfMemory error. I'm aware of the Sorting does have some pretty sell defined memory requirements. Sorting a field builds up a "FieldCache" ... esentailly an array with one slot per document of whatever type you are sorting on, so sorting an index of 15Million docs on an int field takes ~60Megs, string fields get more interesting. There the FieldCache maintains an int[] for each doc, and a String[] for each unique string value ... so sorting your 15M docs by a "category" string field where there are only 10000 category names and they are all about 20 characters would take still only take ~60Megs, but sotring on a "title" field where every doc has a unique title and the average title length is 20 characters would take ~60Megs + ~290Megs If you plan on doing some static warming of your searches using your sorts as newSearcher events (which is a good idea so the first user to do a search after any commit doesn't have to wait a really long time for the FieldCache to be built) you'll need twice that (one FieldCache for the current searcher, one FieldCache for the "on deck" searcher). -Hoss
