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https://issues.apache.org/jira/browse/CASSANDRA-21770?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18129843#comment-18129843
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Brad Schoening commented on CASSANDRA-21770:
--------------------------------------------
Please see
{{[CASSANDRA-17665|https://issues.apache.org/jira/browse/CASSANDRA-17665] Add
nodetool getreplicas}}
> Add node-centric interface for identifying replica peers
> --------------------------------------------------------
>
> Key: CASSANDRA-21770
> URL: https://issues.apache.org/jira/browse/CASSANDRA-21770
> Project: Apache Cassandra
> Issue Type: Improvement
> Components: Feature/Virtual Tables, Tool/nodetool
> Reporter: n.v.harikrishna
> Assignee: n.v.harikrishna
> Priority: Normal
> Fix For: 6.x, 7.x
>
> Attachments: ci_summary.html
>
>
> *Problem*
>
> Operators often need to bounce, upgrade or replace nodes one after another.
> To keep data available, they must not take down a node and the nodes that
> hold copies of the same data (its replica peers) at the same time.
>
> The tools Cassandra has today, such as nodetool describering and nodetool
> getendpoints, are range-centric or key-centric. They answer "which nodes own
> this range or key?" Operators need the node-centric answer: "which nodes
> share data with this node?" To get it now, they have to put it together
> themselves from token ranges, keyspaces and replication settings. This is
> slow and easy to get wrong, especially while nodes are joining or leaving the
> cluster.
>
> *Proposed solution*
>
> Add a node-centric view of replica peers: for each node, list the other nodes
> that share at least one token range with it. Peers are grouped by datacenter.
> Reads and writes are listed separately, because they can differ while nodes
> are joining or leaving. The data comes from the cluster metadata. This view
> is exposed through:
> - A new nodetool command: _nodetool placement peers_. It can filter by node
> (-n), datacenter (-dc) and keyspace (-k / -x). It prints YAML or JSON.
> - A new JMX operation in StorageServiceMBean.
> - A new virtual table, _system_views.replica_peers_, which shows the peers
> of the local node.
> _Sample output:_
> {noformat}
> $ nodetool placement peers
> version: 0
> format_version: 1
> epoch: 9
> keyspaces: [ks1, system_auth, system_cluster_metadata, system_distributed,
> system_traces]
> endpoints: {1: '127.0.0.1:7005', 2: '127.0.0.3:7005', 3: '127.0.0.2:7005'}
> peers: 1:
> read: datacenter1: [2, 3]
> write: datacenter1: [2, 3]
> 2:
> read: datacenter1: [1, 3]
> write: datacenter1: [1, 3]
> 3:
> read: datacenter1: [1, 2]
> write: datacenter1: [1, 2]
> catch_up: SKIPPED
> cms: INITIALIZED
> queried_from: 127.0.0.1:7005
> {noformat}
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