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From "Erick Erickson (JIRA)" <j...@apache.org>
Subject [jira] [Created] (SOLR-9583) When the same <uniqueKey> exists across multiple collections that are searched with an alias, the document returned in the results list is indeterminant
Date Thu, 29 Sep 2016 17:59:20 GMT
Erick Erickson created SOLR-9583:
------------------------------------

             Summary: When the same <uniqueKey> exists across multiple collections that
are searched with an alias, the document returned in the results list is indeterminant
                 Key: SOLR-9583
                 URL: https://issues.apache.org/jira/browse/SOLR-9583
             Project: Solr
          Issue Type: Bug
      Security Level: Public (Default Security Level. Issues are Public)
            Reporter: Erick Erickson


Not quite sure whether to call this a bug or improvement...

Currently if I have two collections C1 and C2 and an alias that points to both _and_ I have
a document in both collections with the _same_ <unkqueKey>, the returned list  sometimes
has the doc from C1 and sometimes from C2.

If I add shards.info=true I see the document found in each collection, but only one in the
document list. Which one changes if I re-submit the identical query.

This seems incorrect, perhaps a side effect of piggy-backing the collection aliasing on searching
multiple shards? (Thanks Shalin for that bit of background).

I can see both use-cases: 

1>  aliasing multiple collections validly assumes that <uniqueKey>s should be unique
across them all and only one doc should be returned. Even in this case which doc should be
returned should be deterministic.

2> these are arbitrary collections without any a-priori relationship and identical <unkqueKey>s
do NOT identify the "same" document so both should be returned.

So I propose we do two things:

a> provide a param for the CREATEALIAS command that controls whether docs with the same
<unkqueKey> from different collections should both be returned. If they both should,
there's still the question of in what order.

b> provide a deterministic way dups from different collections are resolved. What that
algorithm is I'm not quite sure. The order the collections were specified in the CREATEALIAS
command? Some field in the documents? Other??? What happens if this option is not specified
on the CREATEALIAS command?

Implicit in the above is my assumption that it's perfectly valid to have different aliases
in the same cluster behave differently if specified.



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