On Wed, Dec 12, 2012 at 5:49 PM, Michael Ryan <mr...@moreover.com> wrote: > When sorting a TrieLongField, should there be any expected difference in > query speed when sorting ascending vs sorting descending? I'm seeing desc > queries sometimes take 10x longer than asc queries. I can provide more > details if necessary.
Perhaps if there are a lot more ties on one end vs the other? Or of the values being sorted on aren't that random? Do they naturally increase like a timestamp? Docs will collect in the order that the document was indexed (roughly... things can change somewhat due to out-of-order segment merges). So if you sort by a timestamp descending (timestamp when you added the doc), documents collected later will normally be more competitive than any documents collected thus far in the priority queue, causing a lot of flux in said queue. For the ascending case, the first N documents you collect are likely to have the lowest timestamp and hence the priority queue will never change again - it's the optimal case. -Yonik http://lucidworks.com
