Luca Cavanna created LUCENE-5718:
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Summary: More flexible compound queries (containing mtq) support
in postings highlighter
Key: LUCENE-5718
URL: https://issues.apache.org/jira/browse/LUCENE-5718
Project: Lucene - Core
Issue Type: Improvement
Components: modules/highlighter
Affects Versions: 4.8.1
Reporter: Luca Cavanna
The postings highlighter currently pulls the automata from multi term queries
and doesn't require calling rewrite to make highlighting work. In order to do
so it also needs to check whether the query is a compound one and eventually
extract its subqueries. This is currently done in the MultiTermHighlighting
class and works well but has two potential problems:
1) not all the possible compound queries are necessarily supported as we need
to go over each of them one by one (see LUCENE-5717) and this requires keeping
the "switch" up-to-date if new queries gets added to lucene
2) it doesn't support custom compound queries but only the set of queries
available out-of-the-box
I've been thinking about how this can be improved and one of the ideas I came
up with is to introduce a generic way to retrieve the subqueries from compound
queries, like for instance have a new abstract base class with a getLeaves or
getSubQueries method and have all the compound queries extend it. What this
method would do is return a flat array of all the leaf queries that the
compound query is made of.
Not sure whether this would be needed in other places in lucene, but it doesn't
seem like a small change and it would definitely affect (or benefit?) more than
just the postings highlighter support for multi term queries.
In particular the second problem (custom queries) seems hard to solve without a
way to expose this info directly from the query though, unless we want to make
the MultiTermHighlighting#extractAutomata method extensible in some way.
Would like to hear what people think and work on this as soon as we identified
which direction we want to take.
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