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https://issues.apache.org/jira/browse/SOLR-13749?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17053641#comment-17053641
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Kevin Watters commented on SOLR-13749:
--------------------------------------
having a local param like method=xcjf could trigger the xcjf query parser if we
want. There are some complications. Currently, XCJF benefits greatly by some
additional configuration for that query parser to specify the field in which a
collection has been routed on. The current join query parsers aren't defined
by default in the solrconfig.xml . by merging together the functionality of
these 2 query parsers, we might want to explicitly define the join query parser
in the solr config by default.
Additionally, there are many query parsers beyond xcjf that are really join
query parsers.
"child", and "parent" should also be considered "join" query parsers if we want
to fully go to a consolidated join query parser model.
We'll try to be responsive to issues on this ticket, however, I'm not sure how
much bandwidth we will have for larger refactors related to xcjf. My
preference would be that we leave it as is. This is what we were asked to
develop and contribute back so we'd like to keep it as close to the original
contribution as possible. If we collectively want to wrangle all of those join
parsers into a single consolidated join query parser perhaps we could track
that as a different issue/ticket.
> Implement support for joining across collections with multiple shards ( XCJF )
> ------------------------------------------------------------------------------
>
> Key: SOLR-13749
> URL: https://issues.apache.org/jira/browse/SOLR-13749
> Project: Solr
> Issue Type: New Feature
> Reporter: Kevin Watters
> Assignee: Gus Heck
> Priority: Major
> Fix For: 8.5
>
> Time Spent: 1.5h
> Remaining Estimate: 0h
>
> This ticket includes 2 query parsers.
> The first one is the "Cross collection join filter" (XCJF) parser. This is
> the "Cross-collection join filter" query parser. It can do a call out to a
> remote collection to get a set of join keys to be used as a filter against
> the local collection.
> The second one is the Hash Range query parser that you can specify a field
> name and a hash range, the result is that only the documents that would have
> hashed to that range will be returned.
> This query parser will do an intersection based on join keys between 2
> collections.
> The local collection is the collection that you are searching against.
> The remote collection is the collection that contains the join keys that you
> want to use as a filter.
> Each shard participating in the distributed request will execute a query
> against the remote collection. If the local collection is setup with the
> compositeId router to be routed on the join key field, a hash range query is
> applied to the remote collection query to only match the documents that
> contain a potential match for the documents that are in the local shard/core.
>
>
> Here's some vocab to help with the descriptions of the various parameters.
> ||Term||Description||
> |Local Collection|This is the main collection that is being queried.|
> |Remote Collection|This is the collection that the XCJFQuery will query to
> resolve the join keys.|
> |XCJFQuery|The lucene query that executes a search to get back a set of join
> keys from a remote collection|
> |HashRangeQuery|The lucene query that matches only the documents whose hash
> code on a field falls within a specified range.|
>
>
> ||Param ||Required ||Description||
> |collection|Required|The name of the external Solr collection to be queried
> to retrieve the set of join key values ( required )|
> |zkHost|Optional|The connection string to be used to connect to Zookeeper.
> zkHost and solrUrl are both optional parameters, and at most one of them
> should be specified.
> If neither of zkHost or solrUrl are specified, the local Zookeeper cluster
> will be used. ( optional )|
> |solrUrl|Optional|The URL of the external Solr node to be queried ( optional
> )|
> |from|Required|The join key field name in the external collection ( required
> )|
> |to|Required|The join key field name in the local collection|
> |v|See Note|The query to be executed against the external Solr collection to
> retrieve the set of join key values.
> Note: The original query can be passed at the end of the string or as the
> "v" parameter.
> It's recommended to use query parameter substitution with the "v" parameter
> to ensure no issues arise with the default query parsers.|
> |routed| |true / false. If true, the XCJF query will use each shard's hash
> range to determine the set of join keys to retrieve for that shard.
> This parameter improves the performance of the cross-collection join, but
> it depends on the local collection being routed by the toField. If this
> parameter is not specified,
> the XCJF query will try to determine the correct value automatically.|
> |ttl| |The length of time that an XCJF query in the cache will be considered
> valid, in seconds. Defaults to 3600 (one hour).
> The XCJF query will not be aware of changes to the remote collection, so
> if the remote collection is updated, cached XCJF queries may give inaccurate
> results.
> After the ttl period has expired, the XCJF query will re-execute the join
> against the remote collection.|
> |_All others_| |Any normal Solr parameter can also be specified as a local
> param.|
>
> Example Solr Config.xml changes:
>
> {{<}}{{cache}} {{name}}{{=}}{{"hash_vin"}}
> {{ }}{{class}}{{=}}{{"solr.LRUCache"}}
> {{ }}{{size}}{{=}}{{"128"}}
> {{ }}{{initialSize}}{{=}}{{"0"}}
> {{ }}{{regenerator}}{{=}}{{"solr.NoOpRegenerator"}}{{/>}}
>
> {{<}}{{queryParser}} {{name}}{{=}}{{"xcjf"}}
> {{class}}{{=}}{{"org.apache.solr.search.join.XCJFQueryParserPlugin"}}{{>}}
> {{ }}{{<}}{{str}} {{name}}{{=}}{{"routerField"}}{{>vin</}}{{str}}{{>}}
> {{</}}{{queryParser}}{{>}}
>
> {{<}}{{queryParser}} {{name}}{{=}}{{"hash_range"}}
> {{class}}{{=}}{{"org.apache.solr.search.join.HashRangeQueryParserPlugin"}}
> {{/>}}
>
> Example Usage:
> {{{!xcjf collection=}}{{"otherCollection"}} {{from=}}{{"fromField"}}
> {{to=}}{{"toField"}} {{v=}}{{"**:**"}}{{}}}
>
>
>
>
>
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