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From "Stephen Yuan Jiang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-18036) Data locality is not maintained after cluster restart or SSH
Date Fri, 12 May 2017 20:58:05 GMT

    [ https://issues.apache.org/jira/browse/HBASE-18036?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16008684#comment-16008684

Stephen Yuan Jiang commented on HBASE-18036:

The V1 patch has minor change based on [~elserj]'s feedback.  Also add some logging to make
the change clear.

Next up: I will use the same logic in branch-1 and other child branches.  Base on [~devaraj]'s
offline feedback, I will remove the newly introduced "hbase.master.retain.assignment" config
in branch-1; but keep the config in other branches (this config is just for in case of regression,
user has a way to revert back to original round robin behavior; as patch releases usually
don't have full testing)

> Data locality is not maintained after cluster restart or SSH
> ------------------------------------------------------------
>                 Key: HBASE-18036
>                 URL: https://issues.apache.org/jira/browse/HBASE-18036
>             Project: HBase
>          Issue Type: Bug
>          Components: Region Assignment
>    Affects Versions: 1.4.0, 1.3.1, 1.2.5, 1.1.10
>            Reporter: Stephen Yuan Jiang
>            Assignee: Stephen Yuan Jiang
>         Attachments: HBASE-18036.v0-branch-1.1.patch, HBASE-18036.v1-branch-1.1.patch
> After HBASE-2896 / HBASE-4402, we think data locality is maintained after cluster restart.
 However, we have seem some complains about data locality loss when cluster restart (eg. HBASE-17963).
> Examining the AssignmentManager#processDeadServersAndRegionsInTransition() code,  for
cluster start, I expected to hit the following code path:
> {code}
>     if (!failover) {
>       // Fresh cluster startup.
>       LOG.info("Clean cluster startup. Assigning user regions");
>       assignAllUserRegions(allRegions);
>     }
> {code}
> where assignAllUserRegions would use retainAssignment() call in LoadBalancer; however,
from master log,  we usually hit the failover code path:
> {code}
>     // If we found user regions out on cluster, its a failover.
>     if (failover) {
>       LOG.info("Found regions out on cluster or in RIT; presuming failover");
>       // Process list of dead servers and regions in RIT.
>       // See HBASE-4580 for more information.
>       processDeadServersAndRecoverLostRegions(deadServers);
>     }
> {code}
> where processDeadServersAndRecoverLostRegions() would put dead servers in SSH and SSH
uses roundRobinAssignment() in LoadBalancer.  That is why we would see loss locality more
often than retaining locality during cluster restart.
> Note: the code I was looking at is close to branch-1 and branch-1.1.

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