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https://issues.apache.org/jira/browse/IGNITE-24104?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Vadim Pakhnushev reassigned IGNITE-24104:
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Assignee: Vadim Pakhnushev
> Add the new distribution zone parameter QUORUM_SIZE
> ---------------------------------------------------
>
> Key: IGNITE-24104
> URL: https://issues.apache.org/jira/browse/IGNITE-24104
> Project: Ignite
> Issue Type: Improvement
> Reporter: Denis Chudov
> Assignee: Vadim Pakhnushev
> Priority: Major
> Labels: ignite-3
>
> *Motivation*
> Quorum is chosen because it is quite straightforward for the user: if they
> are able to keep QUORUM_SIZE nodes in the zone, there should be no data loss,
> unless they lose multiple nodes simultaneously so that the quorum would be
> not able to transfer to nodes that remain online.
> It specifies the size of the majority quorum. In fact, the size of consensus
> group can be derived from it, depending on the replication algorithm, in the
> case of Raft it is calculated as QUORUM_SIZE * 2 - 1, so the quorum size is
> the size of the majority of nodes in the consensus of a replication group.
> This implies that the size of the consensus group will be an odd number, if
> there are enough replicas.
> The QUORUM_SIZE parameter may be set with any sufficient number of replicas,
> either ALL or not. This means that we can have, for example, 10 data nodes, 7
> replicas and quorum size 3, meaning that 5 replicas will form the consensus
> group and 2 will be learners.
> The default value should be
> * If there are 4 or less data nodes: min(2, data_nodes_count);
> * If there are at least 5 data nodes: 3.
> Lower and upper boundaries:
> * Lower: 1 if there is only one replica and 2 if there is more than 1 node.
> Having the quorum of 1 node where there are more replicas makes no sense and
> decreases reliability;
> * Upper: no less than lower bound, but making the consensus group fit into
> the configured replicas count.
> *Definition of done*
> The QUORUM_SIZE parameter for the zone is added, with aforementioned defaults
> and boundaries. Unit tests for defaults and boundaries are added.
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