[SOLR-13257] Enable replica routing affinity for better cache usage

• Type: New Feature
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 8.3, 9.0
• Component/s: SolrCloud
• Assignee: Anshum Gupta
• Reporter: Michael Gibney
• Created: 15/Feb/19 19:13
• Updated: 12/May/22 00:26
• Resolved: 28/Aug/19 16:47

Description

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 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.

Issue Links

• is duplicated by: SOLR-13258 'sticky' replica affinity support
• is related to: SOLR-6730 select?replicaAffinity=(node|host) and replicaAffinity.hostPriorities support
• links to: GitHub Pull Request #677
• links to: GitHub Pull Request #848
• links to: GitHub Pull Request #849