[jira] [Commented] (SOLR-4905) Allow fromIndex parameter to JoinQParserPlugin to refer to a single-sharded collection that has a replica on all nodes

["Paul Blanchaert (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SOLR-4905?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15001977#comment-15001977 ] 

Paul Blanchaert commented on SOLR-4905:
---------------------------------------

Today, I came across the same issue as reported by Mikhail Khludnev ("SolrCloud join: multiple shards not yet supported join").

I would expect that there is no issue to perform a cross-core join over sharded collections when the following conditions are met:
1) both collections are sharded with the same replicationFactor and numShards
2) router.field of the collection is set to the same "key-field"
3) the cross-core join is based on that same (from/to) "key-field"

The router.field setup ensures that documents with the same "key-field" are routed to the same node. 
So the combination based on the "key-field" should always be available within the same node.

>From a user perspective, I believe these assumptions seem to be the "normal" use-case in the cross-core join.
So, when these assumptions are correct, the next question is probably how feasable it is to implement this logic in the JoinQParserPlugin?

Thanks for your feedback.

> Allow fromIndex parameter to JoinQParserPlugin to refer to a single-sharded collection that has a replica on all nodes
> ----------------------------------------------------------------------------------------------------------------------
>
>                 Key: SOLR-4905
>                 URL: https://issues.apache.org/jira/browse/SOLR-4905
>             Project: Solr
>          Issue Type: Improvement
>          Components: SolrCloud
>            Reporter: Philip K. Warren
>            Assignee: Timothy Potter
>             Fix For: 5.1, Trunk
>
>         Attachments: SOLR-4905.patch, SOLR-4905.patch, 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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