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https://issues.apache.org/jira/browse/SOLR-13257?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16806730#comment-16806730
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Jan Høydahl commented on SOLR-13257:
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I wonder if this perhaps is such a common use case that we could consider
folding it into the default shardHandler as a configuration option.
Also, the {{getReplicaId()}} method looks a bit fragile relying on number
encoded in core name. I think it may break if someone hand-chooses core name.
So please try to pull the replica number from somewhere else.
> Enable replica routing affinity for better cache usage
> ------------------------------------------------------
>
> Key: SOLR-13257
> URL: https://issues.apache.org/jira/browse/SOLR-13257
> Project: Solr
> Issue Type: Improvement
> Security Level: Public(Default Security Level. Issues are Public)
> Components: SolrCloud
> Affects Versions: 7.4, master (9.0)
> Reporter: Michael Gibney
> Priority: Minor
> Attachments: AffinityShardHandlerFactory.java
>
>
> For each shard in a distributed request, Solr currently routes each request
> randomly via
> [ShufflingReplicaListTransformer|https://github.com/apache/lucene-solr/blob/master/solr/core/src/java/org/apache/solr/handler/component/ShufflingReplicaListTransformer.java]
> to a particular replica. In setups with replication factor >1, this normally
> results in a situation where subsequent requests (which one would hope/expect
> to leverage cached results from previous related requests) end up getting
> routed to a replica that hasn't seen any related requests.
> The problem can be replicated by issuing a relatively expensive query (maybe
> containing common terms?). The first request initializes the
> {{queryResultCache}} on the consulted replicas. If replication factor >1 and
> there are a sufficient number of shards, subsequent requests will likely be
> routed to at least one replica that _hasn't_ seen the query before. The
> replicas with uninitialized caches become a bottleneck, and from the client's
> perspective, many subsequent requests appear not to benefit from caching at
> all.
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