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From "Michael Gibney (JIRA)" <>
Subject [jira] [Commented] (SOLR-13257) Enable replica routing affinity for better cache usage
Date Tue, 14 May 2019 17:38:00 GMT


Michael Gibney commented on SOLR-13257:

[PR created|]. This ended up being a bit more
involved than I'd anticipated, because I ended up integrating replica affinity with {{shards.preference}}.
This seemed like the most natural place to add this functionality, and it will allow deterministic
routing to be used in conjunction with other replica routing preferences (as a fallback/tie-breaker).
There's also support for configuring default "base routing" preference in solrconfig.xml.

> Enable replica routing affinity for better cache usage
> ------------------------------------------------------
>                 Key: SOLR-13257
>                 URL:
>             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:
> For each shard in a distributed request, Solr currently routes each request randomly
via [ShufflingReplicaListTransformer|]
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
> 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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