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https://issues.apache.org/jira/browse/SOLR-13257?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16769617#comment-16769617
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Michael Gibney edited comment on SOLR-13257 at 2/15/19 7:25 PM:
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The attached standalone java class provides users the option to configure
replica routing affinity by configuring their {{requestHandler}} with:
{code:xml}
<shardHandlerFactory class="AffinityShardHandlerFactory">
<str name="routingParam">routingHash</str>
<str name="hashParam">q</str>
</shardHandlerFactory>
{code}
The {{routingParam}} allows the user to specify a parameter that will be used
to select a replica by {{routingValIntHash % replicationFactor}}. In the
absence of a {{routingParam}} parameter in the request, the request parameter
configured for {{hashParam}} is used to determine replica routing.
The special value {{DISABLE_DETERMINISTIC_ROUTING}} may be passed as the value
of the configured {{routingParam}} query parameter to explicitly fallback to
default (random) replica routing.
was (Author: mgibney):
The attached standalone java class provides users the option to configure
replica routing affinity by configuring their {{requestHandler}} with:
{code:xml}
<shardHandlerFactory class="AffinityShardHandlerFactory">
<str name="routingParam">routingHash</str>
<str name="hashParam">q</str>
</shardHandlerFactory>
{code}
The {{routingParam}} allows the user to specify a parameter that will be used
to select a replica by {{routingValIntHash % replicationFactor}}. In the
absence of a {{routingParam}} parameter in the request, the request parameter
configured for {{hashParam}} is used to determine replica routing.
The special value `DISABLE_DETERMINISTIC_ROUTING` may be passed as the value of
the configured {{routingParam}} query parameter to explicitly fallback to
default (random) replica routing.
> 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: Major
> 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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