[LUCENE-3426] optimizer for n-gram PhraseQuery

• Type: Improvement
• Status: Closed
• Priority: Trivial
• Resolution: Fixed
• Affects Version/s: 2.9.4, 3.0.3, 3.1, 3.2, 3.3, 3.4, 4.0-ALPHA
• Fix Version/s: 3.5, 4.0-ALPHA
• Component/s: core/search
• Lucene Fields: New
• Assignee: Koji Sekiguchi
• Reporter: Koji Sekiguchi
• Created: 10/Sep/11 14:31
• Updated: 21/Jan/12 23:57
• Resolved: 14/Sep/11 13:07

Description

If 2-gram is used and the length of query string is 4, for example q="ABCD", QueryParser generates (when autoGeneratePhraseQueries is true) PhraseQuery("AB BC CD") with slop 0. But it can be optimized PhraseQuery("AB CD") with appropriate positions.

The idea came from the Japanese paper "N.M-gram: Implementation of Inverted Index Using N-gram with Hash Values" by Mikio Hirabayashi, et al. (The main theme of the paper is different from the idea that I'm using here, though)