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https://issues.apache.org/jira/browse/SOLR-4905?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14049570#comment-14049570
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Jack Lo edited comment on SOLR-4905 at 7/2/14 3:19 AM:
-------------------------------------------------------

I have noticed this issue have been lying around for a year, seems like nobody 
is bother to use JOIN in solrcloud, so I decide to tackle this myself.

A small patch has been uploaded here to allow fromIndex to specify a collection 
under cloud environment. Currently, it works if the fromIndex collection is a 
single shard having at least 1 replica on each node. I am planning to support 
multi-shard collection but not really sure how to do it given I am not that 
familiar with the internal mechanics of solr.

Even if we support multishard, given the current implementation of JoinQParser, 
I think we can only support it when a collection with at least 1 replica of all 
shards physically residing on every node. We need all local IndexSearcher. If 
we need full solrcloud join support, I think we need to revamp JoinQParser or 
make something on a higher level to gather terms collection from remote shards 
on StandardRequestHandler.

By the way, I noticed we haven't use JoinUtil in LUCENE, is there a reason to 
not use it, their implementation seems to be more cleaner than the one in SOLR 
right now, I have no idea what it's doing in JoinQParser


was (Author: jacklo):
Partially make solrcloud join to work

> Cross core joins don't work for SolrCloud collections and/or aliases
> --------------------------------------------------------------------
>
>                 Key: SOLR-4905
>                 URL: https://issues.apache.org/jira/browse/SOLR-4905
>             Project: Solr
>          Issue Type: Improvement
>          Components: SolrCloud
>            Reporter: Philip K. Warren
>         Attachments: patch.txt
>
>
> Using a non-SolrCloud setup, it is possible to perform cross core joins 
> (http://wiki.apache.org/solr/Join). When testing with SolrCloud, however, 
> neither the collection name, alias name (we have created aliases to SolrCloud 
> collections), or the automatically generated core name (i.e. 
> <collection>_shard1_replica1) work as the fromIndex parameter for a 
> cross-core join.



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