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Posted to dev@lucene.apache.org by "Jan Høydahl (JIRA)" <ji...@apache.org> on 2019/07/07 20:59:00 UTC
[jira] [Commented] (SOLR-13257) Enable replica routing affinity for
better cache usage
[ https://issues.apache.org/jira/browse/SOLR-13257?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16879951#comment-16879951 ]
Jan Høydahl commented on SOLR-13257:
------------------------------------
I extracted a patch file from your PR and attached here to trigger automatic patch validation. Hopefully there will be a post from Yetus soon with either +1 or -1 result, which will indicate whether more work is needed on the patch. I also tagged [~tomasflobbe] in the PR as a potential reviewer.
> 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
> Components: SolrCloud
> Affects Versions: 7.4, master (9.0)
> Reporter: Michael Gibney
> Priority: Minor
> Attachments: AffinityShardHandlerFactory.java, SOLR-13257.patch
>
> Time Spent: 10m
> Remaining Estimate: 0h
>
> 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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