Paul Blanchaert created SOLR-8297:
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Summary: Allow join query over 2 sharded collections: enhance
functionality and exception handling
Key: SOLR-8297
URL: https://issues.apache.org/jira/browse/SOLR-8297
Project: Solr
Issue Type: Improvement
Components: SolrCloud
Affects Versions: 5.3
Reporter: Paul Blanchaert
Enhancement based on SOLR-4905. New Jira issue raised as suggested by Mikhail
Khludnev.
A) exception handling:
The exception "SolrCloud join: multiple shards not yet supported" thrown in the
function findLocalReplicaForFromIndex of JoinQParserPlugin is not triggered
correctly: In my use-case, I've a join on a facet.query and when my results are
only found in 1 shard and the facet.query with the join is querying the last
replica of the last slice, then the exception is not thrown.
I believe it's better to verify the nr of slices when we want to verify the
"multiple shards not yet supported" exception (so exception is thrown when
zkController.getClusterState().getSlices(fromIndex).size()>1).
B) functional enhancement:
I would expect that there is no problem 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 collections is set to the same "key-field" (collection
of "fromindex" has router.field = "from" field and collection joined to has
router.field = "to" 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 a "normal"
>use-case in the cross-core join in SolrCloud.
Hope this helps
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