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https://issues.apache.org/jira/browse/SOLR-12495?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16520654#comment-16520654
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Jerry Bao commented on SOLR-12495:
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{quote}
Actually, the terms replica , shard are always associated with a collection. If 
the attribute shard is present , the replica counts are computed on a per-shard 
basis , if it is absent, it is computed on a per-collection basis

The equivalent term for a replica globally is a core which is not associated 
with a collection or shard
{quote}
I see; could {"core": "#MINIMUM", "node": "#ANY"} be included with this issue? 
Along with per-collection balancing, we'll also need cluster-wide balancing.

{quote}
That means The no:of of replicas will have to be between 1 and 2 (inclusive) . 
Which means , both 1 and 2 are valid but 0 , 3 or >3 are invalid and , the list 
of violations will show that
{quote}
Awesome! No qualms here then :)

Thanks for all your help on this issue! Cluster balancing is a critical issue 
for us @ Reddit.

> Enhance the Autoscaling policy syntax to evenly distribute replicas
> -------------------------------------------------------------------
>
>                 Key: SOLR-12495
>                 URL: https://issues.apache.org/jira/browse/SOLR-12495
>             Project: Solr
>          Issue Type: New Feature
>      Security Level: Public(Default Security Level. Issues are Public) 
>          Components: AutoScaling
>            Reporter: Noble Paul
>            Priority: Major
>
> Support a new function value for {{replica= "#MINIMUM"}}
> {{#MINIMUM}} means the minimum computed value for the given configuration
> the value of replica will be calculated as  {{<= 
> Math.ceil(number_of_replicas/number_of_valid_nodes) }}
> *example 1:*
> {code:java}
> {"replica" : "#MINIMUM" , "shard" : "#EACH" , "node" : "#ANY"}
> {code}
> *case 1* : nodes=3, replicationFactor=4
>  the value of replica will be calculated as {{Math.ceil(4/3) = 2}}
> current state : nodes=3, replicationFactor=2
> this is equivalent to the hard coded rule
> {code:java}
> {"replica" : "<3" , "shard" : "#EACH" , "node" : "#ANY"}
> {code}
> *case 2* : 
> current state : nodes=3, replicationFactor=2
> this is equivalent to the hard coded rule
> {code:java}
> {"replica" : "<3" , "shard" : "#EACH" , "node" : "#ANY"}
> {code}
> *example:2*
> {code}
> {"replica" : "#MINIMUM"  , "node" : "#ANY"}{code}
> case 1: numShards = 2, replicationFactor=3, nodes = 5
> this is equivalent to the hard coded rule
> {code:java}
> {"replica" : "<3" , "node" : "#ANY"}
> {code}
> *example:3*
> {code}
> {"replica" : "<2"  , "shard" : "#EACH" , "port" : "8983"}{code}
> case 1: {{replicationFactor=3, nodes with port 8983 = 2}}
> this is equivalent to the hard coded rule
> {code}
> {"replica" : "<3"  , "shard" : "#EACH" , "port" : "8983"}{code}



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