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https://issues.apache.org/jira/browse/LUCENE-3041?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13025173#comment-13025173
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Chris Male commented on LUCENE-3041:
------------------------------------
bq. Regarding sharing the map, I think you should use a prototype pattern that
creates a new Processor from an existing one maybe via clone()? In the
InvocationDispatcher case we should maybe use a concurrent hash map and share
the map across instances for the same dispatcher class.
I don't quite follow you. Currently DispatchingQueryProcessor caches
InvocationDispatchers by concrete impl type. So we only create a new
InvocationDispatcher when we have a new implementation (which means
InvocationDispatchers are shared between segments, searches, everything). In
that regard DispatchingQueryProcessor#dispatcherByClass should be a
ConcurrentHashMap. But otherwise, I think we're okay?
bq. The process implementation in DefaultQueryProcessor executes query.rewrite
before passing the query to the dispatcher which is no good since some
QueryProcessor impls might not want to rewrite that query at all. In
LUCENE-2868 karl tries to find a way to prevent lucene to rewrite one and the
same FuzzyQuery since he has them in multiple clauses somewhere down the BQ
tree. This is a super expensive operation in his case to rewriting it only once
makes sense. I think this should be left to the actual implementation.
This is super tricky. The question is how to define a base case in
#process(Query). Lets assume DefaultQueryProcessor#process(Query) just
dispatched immediately. It might be a receiver of the same dispatch (perhaps
the query is a TermQuery and no #process(TermQuery) is provided, so
#process(Query) is chosen). It then just dispatches again, receives again..
and we're in a loop.
Any thoughts on how to avoid that?
> Support Query Visting / Walking
> -------------------------------
>
> Key: LUCENE-3041
> URL: https://issues.apache.org/jira/browse/LUCENE-3041
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Search
> Reporter: Chris Male
> Priority: Minor
> Attachments: LUCENE-3041.patch
>
>
> Out of the discussion in LUCENE-2868, it could be useful to add a generic
> Query Visitor / Walker that could be used for more advanced rewriting,
> optimizations or anything that requires state to be stored as each Query is
> visited.
> We could keep the interface very simple:
> {code}
> public interface QueryVisitor {
> Query visit(Query query);
> }
> {code}
> and then use a reflection based visitor like Earwin suggested, which would
> allow implementators to provide visit methods for just Querys that they are
> interested in.
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