This API doesn't exist today. Lucene has long needed for queries impls to do this, so that we can properly plan/optimize how the query is run. EG an AND query would use this to pick the more restrictive clause to drive the intersection.
For TermQuery you could just call IR.docFreq? (Doesn't take deletions into account so it'll always be an upper bound). For other queries... you could pull the scorer, iterate over some number of docs, and then "guestimate" based on what docID you got up to vs how many docs you asked for, how many matches there would be for the full index? This would assume matches are uniformly distributed throughout the index (eg, that docs are indexed in random order) which is definitely not the case typically in practice. Mike McCandless http://blog.mikemccandless.com On Tue, Jul 5, 2011 at 2:19 PM, Andres Taylor <andres.tay...@neotechnology.com> wrote: > Hi there, > > A work with Neo4j <http://neo4j.org/>, a NoSQL graph > database tightly coupled with Lucene. I am now working on an optimizing > execution engine. To do this well, I would like to know more about the > existing Lucene indices. Ideally, I'd like to be able to ask a Lucene index > how many hits a query might give me, before I actually run the query. The > answer will probably just be an estimation, but that's fine. > > Is this possible today? > > Best regards, > > Andrés > --------------------------------------------------------------------- To unsubscribe, e-mail: java-user-unsubscr...@lucene.apache.org For additional commands, e-mail: java-user-h...@lucene.apache.org
