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https://issues.apache.org/jira/browse/SOLR-13749?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17147203#comment-17147203
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David Smiley commented on SOLR-13749:
-------------------------------------
As I was browsing through Solr's DocSet related code, I noticed something a
little surprising to me -- CrossCollectionJoinQuery internally uses
{{DocSetUtil.createDocSet(...)}} to get a DocSet instead of
{{SolrIndexSearcher.getDocSet(query)}} --
https://github.com/apache/lucene-solr/blob/54e6528304027ab15bbac2b62746b34eed7b4f40/solr/core/src/java/org/apache/solr/search/join/CrossCollectionJoinQuery.java#L173
DocSetUtil.createDocSet does _not_ use the filter cache whereas
SolrIndexSearcher.getDocSet will (provided you have one and that the query
doesn't declare itself as not being cacheable). IMO to avoid confusion, this
method ought to be inlined into its only caller which is just a one-liner any
way.
Was it intentional that this query not be cached? Perhaps it's debatable and
maybe the query should have a flag for this, since maybe it'd just pollute the
filter cache. Or maybe it's basically always pointless. I hope Dan/Kevin can
respond as you probably have more insights here than I.
Also, it's not evident to me why this join query demands this DocSet
internally.
{{org.apache.solr.search.join.CrossCollectionJoinQuery.JoinKeyCollector#getDocSet}}
exists but couldn't it be {{getQuery}}? The caller ultimately wants a Scorer
so why materialize a DocSet when you could go from {{Query->Weight->Scorer}}?
One answer might be to benefit from a cache, but as I explained, you routed
around it ;-). To produce the Query: In the Terms case, I see you collect the
postings early and thus you have a DocSet so you could call DocSet.getTopFilter
(Filter subclasses Query) and in the numeric case, just return the Query that
you already have. I don't know why the Terms vs Numerics case has to vary so
much here; the Terms case could have been a TermInSetQuery.
> 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: Blocker
> Fix For: 8.6
>
> Attachments: 2020-03 Smiley with ASF hat.jpeg
>
> Time Spent: 2h 40m
> 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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