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Vertica Remove Nodes?

We want to remove some nodes from our cluster. Going through the docs i have understood the process such as follow-
A)Remove node from Database.
B)Remove node from the Cluster.
C)Rebalancing after node removal.
However I need some clarity on the following point mentioned in the doc
https://www.vertica.com/docs/9.2.x/HTML/Content/Authoring/AdministratorsGuide/ManageNodes/RemovingNodesFromADatabase.htm
"When warned that you must redesign your database and create projections that exclude the hosts you going to drop, select Yes"
Our most of the projections are segmented on all nodes,what type of challenges we will face in aspects of projection redesigning.

Answers

  • Jim_KnicelyJim_Knicely Administrator

    Prior the removal of nodes from an Enterprise Mode Vertica database, a process called "Rebalance" has to be run so that any data on nodes to be removed is distributed to the remaining nodes per the segementation clause on on each projection.

    Some helpful links:
    Best Practices for Preparing Your Cluster for Rebalance
    Understanding Rebalancing, Part 1: What Happens During Rebalancing
    Understanding Rebalancing, Part 2: Optimizing for Rebalancing

  • SK21SK21

    Hello @Jim_Knicely Rebalacing doc states after you remove or add node do rebalance.
    So according to your comment we must do rebalance prior and after node removal?
    Also i have noticed 13 nodes out of 21 nodes in my cluster contains 1 TB data each.
    While other 8 nodes contains 0.7 TB of data each. WIll rebalance also help here?

  • Jim_KnicelyJim_Knicely Administrator
    edited May 14

    @SK21 - How are you removing nodes? MC or admintools? If either, Vertica will initiate the rebalance for you. If you are doing this manually, you have to set the nodes to be EPHEMERAL, then run the REBALANCE_CLUSTER function.

    Per the question "WIll rebalance also help here":

    If your nodes only have 1 TB or less per node, then you have way too many nodes in your cluster :) Anyway, no, a rebalance won't help as there is skew in your data. Take a look at the segmentation clauses of the projections.

  • SK21SK21

    Thanks @Jim_Knicely , i will use admintools utility
    So things can be summarise in 2 steps-
    A)Remove node from a Database.
    B)Remove node from a cluster.........No rebalancing prior or after?
    Is this so? your second comment on this post about rebalancing has made me little confused.

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