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From "Michael McCandless (JIRA)" <>
Subject [jira] [Commented] (LUCENE-3171) BlockJoinQuery/Collector
Date Sun, 26 Jun 2011 15:11:47 GMT


Michael McCandless commented on LUCENE-3171:

bq. The possible inefficiency is the same as the one for a any sparsely filled OpenBitSet.

Ahh, OK.  Though, I suspect this (the linear scan OBS does for next/prevSetBit) is a minor
cost overall, if indeed the app has so many child docs per parent that a sparse bit set would
be warranted?  Ie, the Query/Collector would still be visiting these many child docs per parent,
I guess?  (Unless the query hits few results).

I don't think a jdoc warning is really required for this... but I'm fine if you want to add

I'll commit this soon and resolve LUCENE-2454 as duplicate!

> BlockJoinQuery/Collector
> ------------------------
>                 Key: LUCENE-3171
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: modules/other
>            Reporter: Michael McCandless
>             Fix For: 3.3, 4.0
>         Attachments: LUCENE-3171.patch, LUCENE-3171.patch, LUCENE-3171.patch
> I created a single-pass Query + Collector to implement nested docs.
> The approach is similar to LUCENE-2454, in that the app must index
> documents in "join order", as a block (IW.add/updateDocuments), with
> the parent doc at the end of the block, except that this impl is one
> pass.
> Once you join at indexing time, you can take any query that matches
> child docs and join it up to the parent docID space, using
> BlockJoinQuery.  You then use BlockJoinCollector, which sorts parent
> docs by provided Sort, to gather results, grouped by parent; this
> collector finds any BlockJoinQuerys (using Scorer.visitScorers) and
> retains the child docs corresponding to each collected parent doc.
> After searching is done, you retrieve the TopGroups from a provided
> BlockJoinQuery.
> Like LUCENE-2454, this is less general than the arbitrary joins in
> Solr (SOLR-2272) or parent/child from ElasticSearch
> (, since you
> must do the join at indexing time as a doc block, but it should be
> able to handle nested joins as well as joins to multiple tables,
> though I don't yet have test cases for these.
> I put this in a new Join module (modules/join); I think as we
> refactor join impls we should put them here.

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