[LUCENE-1644] Enable MultiTermQuery's constant score mode to also use BooleanQuery under the hood

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 2.9
• Component/s: core/search
• Lucene Fields: New
• Assignee: Michael McCandless
• Reporter: Michael McCandless
• Created: 19/May/09 13:03
• Updated: 28/Aug/22 12:01
• Resolved: 25/Jul/09 00:03

Description

When MultiTermQuery is used (via one of its subclasses, eg
WildcardQuery, PrefixQuery, FuzzyQuery, etc.), you can ask it to use
"constant score mode", which pre-builds a filter and then wraps that
filter as a ConstantScoreQuery.

If you don't set that, it instead builds a [potentially massive]
BooleanQuery with one SHOULD clause per term.

There are some limitations of this approach:

• The scores returned by the BooleanQuery are often quite
  meaningless to the app, so, one should be able to use a
  BooleanQuery yet get constant scores back. (Though I vaguely
  remember at least one example someone raised where the scores were
  useful...).

• The resulting BooleanQuery can easily have too many clauses,
  throwing an extremely confusing exception to newish users.

• It'd be better to have the freedom to pick "build filter up front"
  vs "build massive BooleanQuery", when constant scoring is enabled,
  because they have different performance tradeoffs.

• In constant score mode, an OpenBitSet is always used, yet for
  sparse bit sets this does not give good performance.

I think we could address these issues by giving BooleanQuery a
constant score mode, then empower MultiTermQuery (when in constant
score mode) to pick & choose whether to use BooleanQuery vs up-front
filter, and finally empower MultiTermQuery to pick the best (sparse vs
dense) bit set impl.