Using fromIndex for single collection

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Using fromIndex for single collection

Ирина Камалова
I suppose my question is very simple.
Am I right that if I want to use joins in the single collection in
SolrCloud across several shards,
I need to use semantic "fromIndex"?
According to documentation I should use it only if I have different
collections.
I have one single collection across multiple shards and I didn't find a way
to join documents correctly, but with "fromIndex" semantic.

Am I correct?

Best regards,
Irina Kamalova
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Re: Using fromIndex for single collection

Jason Gerlowski
Hi Irina,

Yes, the "fromIndex" parameter can be used to perform a join from the
host collection to a separate, single-shard collection in SolrCloud.
If specified, this "fromIndex" collection must be present on whichever
host is processing the request.  (Often this involves over-replicating
your "fromIndex" so that it's co-located with the other involved
collection).

Additionally, Solr has recently gained support for "Cross Collection
Joins".  This separate approach to joining avoids the restrictions
mentioned above.  This is documented here:
https://lucene.apache.org/solr/guide/8_6/other-parsers.html#cross-collection-join

Best,

Jason

On Wed, Oct 7, 2020 at 12:45 PM Irina Kamalova <[hidden email]> wrote:

>
> I suppose my question is very simple.
> Am I right that if I want to use joins in the single collection in
> SolrCloud across several shards,
> I need to use semantic "fromIndex"?
> According to documentation I should use it only if I have different
> collections.
> I have one single collection across multiple shards and I didn't find a way
> to join documents correctly, but with "fromIndex" semantic.
>
> Am I correct?
>
> Best regards,
> Irina Kamalova