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https://issues.apache.org/jira/browse/LUCENE-3602?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13189316#comment-13189316
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Martijn van Groningen commented on LUCENE-3602:
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bq. Sweet! How join would work in distributed mode, that would be very useful
for BigData projects.
The join is actually executed in a two pass search. During the first pass
search all the terms are gathered for the matching documents based on the
fromQuery. In the second pass search all documents are collected that match
with the gather terms for a specific field. To only way I currently see how
this can work in a distributed environment is that all machines in the cluster
execute the first pass search and then copy the collected terms between
machines. After this is done each machine can execute the second pass. If your
data allows it, you can partition data in your cluster this allows you to skip
the copying of terms.
Currently the api is just one static method and assumes that the joining
happens locally. I think we need to have two more methods. One method that
returns the first pass terms and one method that constructs a query based on
terms from the first pass.
Robert: Yes I see that 3.x MTQ isn't as great as MTQ in trunk. Maybe we need a
different approach (not use MTQ)? The api is clean for users, and allows us to
do joining different in 3x. I'll start backporting and see how well it goes.
> 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
> Fix For: 3.6, 4.0
>
> Attachments: LUCENE-3602.patch, LUCENE-3602.patch, LUCENE-3602.patch,
> LUCENE-3602.patch, LUCENE-3602.patch, LUCENE-3602.patch, LUCENE-3602.patch,
> LUCENE-3602.patch, 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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