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From "Shawn Walker (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-4353) Stabilize tablet assignment during transient failure
Date Fri, 24 Jun 2016 03:30:17 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-4353?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15347620#comment-15347620
] 

Shawn Walker commented on ACCUMULO-4353:
----------------------------------------

It's not so much the cost of performing assignments which is a worry, as the cost of rebalancing
when a tserver comes back.  But these concerns aren't independent.  By blocking premature
reassignment (at some cost to availability), the cost of rebalancing is saved.  Particularly
in something like a rolling restart, where we can expect that a tserver's death will be short-lived,
and that the tserver will not die again after it revives.

> Stabilize tablet assignment during transient failure
> ----------------------------------------------------
>
>                 Key: ACCUMULO-4353
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-4353
>             Project: Accumulo
>          Issue Type: Improvement
>            Reporter: Shawn Walker
>            Assignee: Shawn Walker
>            Priority: Minor
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> When a tablet server dies, Accumulo attempts to reassign the tablets it was hosting as
quickly as possible to maintain availability.  If multiple tablet servers die in quick succession,
such as from a rolling restart of the Accumulo cluster or a network partition, this behavior
can cause a storm of reassignment and rebalancing, placing significant load on the master.
> To avert such load, Accumulo should be capable of maintaining a steady tablet assignment
state in the face of transient tablet server loss.  Instead of reassigning tablets as quickly
as possible, Accumulo should be await the return of a temporarily downed tablet server (for
some configurable duration) before assigning its tablets to other tablet servers.



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