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Date: Wed, 22 May 2013 22:50:19 +0000 (UTC)
From: "Josh Elser (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (ACCUMULO-1454) Need good way to perform a
 rolling restart of all tablet servers
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    [ https://issues.apache.org/jira/browse/ACCUMULO-1454?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13664635#comment-13664635 ] 

Josh Elser commented on ACCUMULO-1454:
--------------------------------------

I think there's more to it than just pausing the balancer.

When a tserver dies, you get a massive swath of tablets that need to be reassigned. While this typically isn't an interruption of service due to the resiliency of the client, it will still affect query response time.

What if there were a way to "decomission" a tserver in which we more gracefully migrate tablets off of that tserver to others. This makes things more difficult on our end; however, it should result in better QOS for clients. For most cases, we could even do neat stuff like wait for all scans to cease for a tablet before we migrate it away.
                
> Need good way to perform a rolling restart of all tablet servers
> ----------------------------------------------------------------
>
>                 Key: ACCUMULO-1454
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-1454
>             Project: Accumulo
>          Issue Type: Improvement
>          Components: tserver
>    Affects Versions: 1.5.0, 1.4.3
>            Reporter: Mike Drob
>
> When needing to change a tserver parameter (e.g. java heap space) across the entire cluster, there is not a graceful way to perform a rolling restart.
> The naive approach of just killing tservers one at a time causes a lot of churn on the cluster as tablets move around and zookeeper tries to maintain current state.
> Potential solutions might be via a fancy fate operation, with coordination by the master. Ideally, the master would know which servers are 'safe' to restart and could minimize overall impact during the operation.

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