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https://issues.apache.org/jira/browse/IGNITE-18879?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Vyacheslav Koptilin updated IGNITE-18879:
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Epic Link: (was: IGNITE-18524)
> Leaseholder candidates balancing
> --------------------------------
>
> Key: IGNITE-18879
> URL: https://issues.apache.org/jira/browse/IGNITE-18879
> Project: Ignite
> Issue Type: Improvement
> Reporter: Denis Chudov
> Priority: Major
> Labels: ignite-3
>
> *Motivation*
> Primary replicas (leaseholders) should be evenly distributed over cluster to
> balance the transactional load between nodes. As the placement driver assigns
> primary replicas, balancing the primary replicas is also it's responsibility.
> Naive implementation of balancing should choose a node as leaseholder
> candidate in a way to save even lease distribution over all nodes. In real
> cluster, it may take into account slow nodes, hot table records, etc. If
> lease candidate declines LeaseGrantMessage from placement driver, the
> balancer should make decision to choose another candidate for given primary
> replica or enforce the previously chosen. So the balancing algorith should be
> pluggable, so that we could have ability to improve/replace/compare it with
> others.
> *Definition of done*
> Introduced interface for lease candidates balancer, and a simple
> implementation sustaining even lease distribution, which is used by placement
> driver by default. No public or internal configuration needed on this stage.
> *Implementation notes*
> Lease candidates balancer should have at least 2 methods:
> - {_}get(group, ignoredNodes){_}: returns candidate for the given group, a
> node from ignoredNodes set can't be chosen as a candidate
> - {_}considerRedirectProposal(group, candidate, proposedCandidate){_}:
> processes redirect proposal for given group provided by given candidate
> (previously chosen using _get_ method), proposedCandidate is the alternative
> candidate. Returns candidate that should be enforced by placement driver.
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