[SOLR-12495] Enhance the Autoscaling policy syntax to evenly distribute replicas among nodes

• Type: New Feature
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 7.5, 8.0
• Component/s: AutoScaling
• Assignee: Noble Paul
• Reporter: Noble Paul
• Created: 19/Jun/18 03:45
• Updated: 08/Jun/19 15:00
• Resolved: 18/Jul/18 12:59

Description

Support a new function value for replica= "#EQUAL"

#EQUAL means the equal no:of replicas on each "node"
the value of replica will be calculated as  <= Math.ceil(number_of_replicas/number_of_valid_nodes) 

example 1:

{"replica" : "#EQUAL" , "shard" : "#EACH" , "node" : "#ANY"}

case 1 : nodes=3, replicationFactor=4
the value of replica will be calculated as Math.ceil(4/3) = 1.33

current state : nodes=3, replicationFactor=2

this is equivalent to the hard coded rule

{"replica" : "<3" , "shard" : "#EACH" , "node" : "#ANY"}

case 2 : 
current state : nodes=3, replicationFactor=2

this is equivalent to the hard coded rule

{"replica" : "<3" , "shard" : "#EACH" , "node" : "#ANY"}

example:2

{"replica" : "#EQUAL"  , "node" : "#ANY"}

case 1: numShards = 2, replicationFactor=3, nodes = 5

this is equivalent to the hard coded rule

{"replica" : "1.2" , "node" : "#ANY"}

Issue Links

• relates to: SOLR-9735 Umbrella JIRA for Auto Scaling and Cluster Management in SolrCloud
• requires: SOLR-12511 Support non integer values for replica in autoscaling rules