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From Tomás Fernández Löbbe (JIRA) <j...@apache.org>
Subject [jira] [Commented] (SOLR-13257) Enable replica routing affinity for better cache usage
Date Wed, 10 Jul 2019 23:03:00 GMT

    [ https://issues.apache.org/jira/browse/SOLR-13257?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16882505#comment-16882505
] 

Tomás Fernández Löbbe commented on SOLR-13257:
----------------------------------------------

This feature sounds great. I left some comments in the PR (not sure if the PR has the latest
patch or not)

> Enable replica routing affinity for better cache usage
> ------------------------------------------------------
>
>                 Key: SOLR-13257
>                 URL: https://issues.apache.org/jira/browse/SOLR-13257
>             Project: Solr
>          Issue Type: New Feature
>          Components: SolrCloud
>            Reporter: Michael Gibney
>            Priority: Minor
>         Attachments: AffinityShardHandlerFactory.java, SOLR-13257.patch, SOLR-13257.patch
>
>          Time Spent: 50m
>  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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