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https://issues.apache.org/jira/browse/LUCENE-3602?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13167865#comment-13167865
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Martijn van Groningen commented on LUCENE-3602:
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bq. You mean the app sometimes actually uses the fromSearcher.fromQuery's
results, directly, without joining?
Yes. In the case of Solr it is checking the filter cache.
bq. but what worries me is just how slow this non-RAM version will be.
I have been running the JoinQuery on my test data set (10.1 M docs) and it
isn't as bad as I expect it would be. This data set contains 100000 products
each product having 100 offers. The JoinQuery with a *:* query as fromQuery
takes about 900 ms and a fromQuery selecting all products with a specific
keyword takes about 350 ms. I think this specific query implementation is
suitable for environments where RAM might be scarce. The RAM version should be
the default.
bq. Stepping back a bit... do we know how this impl compares to how
ElasticSearch does joins? And to how Solr does...?
ES only has index time joining, right? Solr basically uses the same mechanism
as the JoinQuery in this patch, but a bit smarter. It tries to cache the from
term to to term lookup (see JoinQParserPlugin.java line 367). I couldn't port
this part to joining module since this caching relies heavily on the
SolrIndexSearcher.
> Add join query to Lucene
> ------------------------
>
> Key: LUCENE-3602
> URL: https://issues.apache.org/jira/browse/LUCENE-3602
> Project: Lucene - Java
> Issue Type: New Feature
> Components: modules/join
> Reporter: Martijn van Groningen
> Attachments: LUCENE-3602.patch, LUCENE-3602.patch
>
>
> Solr has (psuedo) join query for a while now. I think this should also be
> available in Lucene.
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