[jira] [Created] (SOLR-13258) 'sticky' replica affinity support

["Christine Poerschke (JIRA)" <ji...@apache.org>]

Christine Poerschke created SOLR-13258:
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             Summary: 'sticky' replica affinity support
                 Key: SOLR-13258
                 URL: https://issues.apache.org/jira/browse/SOLR-13258
             Project: Solr
          Issue Type: New Feature
            Reporter: Christine Poerschke



Creating this ticket as both similar to and different from the SOLR-6730 {{select?replicaAffinity=(node|host) and replicaAffinity.hostPriorities support}} ticket.

copy/paste-ing a potential approach from the https://issues.apache.org/jira/browse/SOLR-6730?focusedCommentId=15583110&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-15583110 update:
{quote}
* Two numeric parameters ('seed' and 'mod') are optionally added to each request.
* The two parameters 'place' the requests within the cloud, e.g. for {{mod=9}} any seed between 0 and 8 would be valid and {{seed=6}} would 'place' the request with the 7th of 9 replicas, or more realistically the 3rd of 3 replicas.
* seed-plus-mod placement automatically adjusts when the number of replicas changes i.e. (seed=2,mod=6) would be 3rd-of-6 or 2nd-of-4 or 2nd-of-3 or 1st-of-2 placement.
{quote}

selected code areas of interest:
* The HttpShardHandler's prepDistributed method calls the HttpShardHandlerFactory's getReplicaListTransformer method.
** https://github.com/apache/lucene-solr/blob/releases/lucene-solr/7.7.0/solr/core/src/java/org/apache/solr/handler/component/HttpShardHandler.java#L294
** https://github.com/apache/lucene-solr/blob/releases/lucene-solr/7.7.0/solr/core/src/java/org/apache/solr/handler/component/HttpShardHandlerFactory.java#L438-L484
* The simplest replica list transformer is a shuffling one. Additionally and optionally node preference rules may be applied.
** https://github.com/apache/lucene-solr/blob/releases/lucene-solr/7.7.0/solr/core/src/java/org/apache/solr/handler/component/ShufflingReplicaListTransformer.java



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