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  1. Couchbase Documentation
  2. DOC-8794

Swap Rebalance behaviour clarification

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Details

    • Bug
    • Status: Resolved
    • Major
    • Resolution: Unresolved
    • 6.6.0
    • None
    • core-server
    • None
    • DOC-2021-Jul18-S14
    • 1

    Description

      In the docs on Swap Rebalance (https://docs.couchbase.com/server/current/learn/clusters-and-availability/rebalance.html, and https://docs.couchbase.com/server/current/install/upgrade-online.html#swap-rebalance-example) it would be worth mentioning that Active data is moved between the nodes being swapped, but replicas still need to be rebuilt (this means that there is some data transfer between nodes not being swapped).

      This is important to highlight, since in the UI when rebalance progress is shown, you can see items leaving the nodes not involved in the swap rebalance.

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          tony.hillman Tony Hillman added a comment -

          I've added the following paragraph to the new Swap Rebalance discussion:

           

          Note also that swap rebalance performed with outgoing and incoming Data-Service nodes does involve data-copying from other Data-Service nodes on the cluster. This is because replica vBuckets are created by means of streaming from their corresponding active vBuckets: streaming cannot proceed from a replica vBucket. Consequently, whereas the active vBuckets for an incoming node can be streamed from the corresponding active vBuckets on the outgoing node; the replica vBuckets for an incoming node must be streamed from the corresponding active vBuckets elsewhere on the cluster.

          This is part of the fix for DOC-8793, and can be found at https://github.com/couchbase/docs-server/pull/2049

          tony.hillman Tony Hillman added a comment - I've added the following paragraph to the new Swap Rebalance discussion:   Note also that swap rebalance performed with outgoing and incoming Data-Service nodes  does  involve data-copying from other Data-Service nodes on the cluster. This is because replica vBuckets are created by means of  streaming  from their corresponding active vBuckets: streaming  cannot  proceed from a replica vBucket. Consequently, whereas the active vBuckets for an incoming node can be streamed from the corresponding active vBuckets on the outgoing node; the replica vBuckets for an incoming node must be streamed from the corresponding active vBuckets elsewhere on the cluster. This is part of the fix for DOC-8793 , and can be found at  https://github.com/couchbase/docs-server/pull/2049

          People

            tony.hillman Tony Hillman
            tim.bradgate Tim Bradgate (Inactive)
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              Updated:

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