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https://issues.apache.org/jira/browse/SOLR-8234?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Tom Winch updated SOLR-8234:
----------------------------
    Description: 
This issue describes a MergeStrategy implementation (DJoin) to facilitate 
federated search - that is, distributed search over documents stored in 
separated instances of SOLR (for example, one server per continent), where a 
single document (identified by an agreed, common unique id) may be stored in 
more than one server instance, with (possibly) differing fields and data.

When the MergeStrategy is used in a request handler (via the included QParser) 
in combination with distributed search (shards=), documents having an id that 
has already been seen are not discarded (as per the default behaviour) but, 
instead, are collected and returned as a group of documents all with the same 
id taking a single position in the result set (this is implemented using 
parent/child documents).

Documents are sorted in the result set based on the highest ranking document 
with the same id. It is possible for a document ranking high in one shard to 
rank very low on another shard. As a consequence of this, all shards must be 
asked to return the fields for every document id in the result set (not just of 
those documents they returned), so that all the component parts of each 
document in the search result set are returned.

This issue combines with others to provide full federated search support. See 
also SOLR-8235 and SOLR-8236.

--

Note that this is part of a new implementation of federated search as opposed 
to the older issues SOLR-3799 through SOLR-3805.

  was:
This issue describes a MergeStrategy implementation (DJoin) to facilitate 
federated search - that is, distributed search over documents stored in 
separated instances of SOLR (for example, one server per continent), where a 
single document (identified by an agreed, common unique id) may be stored in 
more than one server instance, with (possibly) differing fields and data.

When the MergeStrategy is used in a request handler (via the included QParser) 
in combination with distributed search (shards=), documents having an id that 
has already been seen are not discarded (as per the default behaviour) but, 
instead, are collected and returned as a group of documents all with the same 
id taking a single position in the result set (this is implemented using 
parent/child documents).

Documents are sorted in the result set based on the highest ranking document 
with the same id. It is possible for a document ranking high in one shard to 
rank very low on another shard. As a consequence of this, all shards must be 
asked to return the fields of for every document id in the result set (not just 
of those documents they returned), so that all the component parts of each 
document in the search result set are returned.

This issue combines with others to provide full federated search support. See 
also SOLR-8235 and SOLR-8236.

--

Note that this is part of a new implementation of federated search as opposed 
to the older issues SOLR-3799 through SOLR-3805.


> Federated Search (new) - DJoin
> ------------------------------
>
>                 Key: SOLR-8234
>                 URL: https://issues.apache.org/jira/browse/SOLR-8234
>             Project: Solr
>          Issue Type: New Feature
>            Reporter: Tom Winch
>            Priority: Minor
>              Labels: federated_search
>             Fix For: 4.10.3
>
>
> This issue describes a MergeStrategy implementation (DJoin) to facilitate 
> federated search - that is, distributed search over documents stored in 
> separated instances of SOLR (for example, one server per continent), where a 
> single document (identified by an agreed, common unique id) may be stored in 
> more than one server instance, with (possibly) differing fields and data.
> When the MergeStrategy is used in a request handler (via the included 
> QParser) in combination with distributed search (shards=), documents having 
> an id that has already been seen are not discarded (as per the default 
> behaviour) but, instead, are collected and returned as a group of documents 
> all with the same id taking a single position in the result set (this is 
> implemented using parent/child documents).
> Documents are sorted in the result set based on the highest ranking document 
> with the same id. It is possible for a document ranking high in one shard to 
> rank very low on another shard. As a consequence of this, all shards must be 
> asked to return the fields for every document id in the result set (not just 
> of those documents they returned), so that all the component parts of each 
> document in the search result set are returned.
> This issue combines with others to provide full federated search support. See 
> also SOLR-8235 and SOLR-8236.
> --
> Note that this is part of a new implementation of federated search as opposed 
> to the older issues SOLR-3799 through SOLR-3805.



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