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From "Noble Paul (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (SOLR-11985) Allow percentage in replica attribute in policy
Date Wed, 20 Jun 2018 15:00:00 GMT

     [ https://issues.apache.org/jira/browse/SOLR-11985?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Noble Paul updated SOLR-11985:
------------------------------
    Attachment:     (was: SOLR-11985.patch)

> Allow percentage in replica attribute in policy
> -----------------------------------------------
>
>                 Key: SOLR-11985
>                 URL: https://issues.apache.org/jira/browse/SOLR-11985
>             Project: Solr
>          Issue Type: Sub-task
>      Security Level: Public(Default Security Level. Issues are Public) 
>          Components: AutoScaling, SolrCloud
>            Reporter: Shalin Shekhar Mangar
>            Assignee: Noble Paul
>            Priority: Major
>             Fix For: master (8.0), 7.5
>
>         Attachments: SOLR-11985.patch, SOLR-11985.patch
>
>
> Today we can only specify an absolute number in the 'replica' attribute in the policy
rules. It'd be useful to write a percentage value to make certain use-cases easier. For example:
> {code:java}
> // Keep a third of the the replicas of each shard in east region
> {"replica" : "<34%", "shard" : "#EACH", "sysprop:region": "east"}
> // Keep two thirds of the the replicas of each shard in west region
> {"replica" : "<67%", "shard" : "#EACH", "sysprop:region": "west"}
> {code}
> Today the above must be represented by different rules for each collection if they have
different replication factors. Also if the replication factor changes later, the absolute
value has to be changed in tandem. So expressing a percentage removes both of these restrictions.
> This feature means that the value of the attribute {{"replica"}} is only available just
in time. We call such values {{"computed values"}} . The computed value for this attribute
depends on other attributes as well. 
>  Take the following 2 rules
> {code:java}
> //example 1
> {"replica" : "<34%", "shard" : "#EACH", "sysprop:region": "east"}
> //example 2
> {"replica" : "<34%",  "sysprop:region": "east"}
> {code}
> assume we have collection {{"A"}} with 2 shards and {{replicationFactor=3}}
> *example 1* would mean that the value of replica is computed as
> {{3 * 34 / 100 = 1.02}}
> Which means *_for each shard_* keep less than 1.02 replica in east availability zone
>  
> *example 2* would mean that the value of replica is computed as 
> {{3 * 2 * 34 / 100 = 2.04}}
>  
> which means _*for each collection*_ keep less than 2.04 replicas on east availability
zone



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