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From "Jeffrey Zhong (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-11059) ZK-less region assignment
Date Tue, 10 Jun 2014 21:53:03 GMT

    [ https://issues.apache.org/jira/browse/HBASE-11059?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14027087#comment-14027087

Jeffrey Zhong commented on HBASE-11059:

I have reviewed the patch v2.1 in high level. Looks great in general. I have following comments:

1)  Rolling restart when turn hbase.assignment.usezk from ON to OFF. 
At this scenario, rolling restart seems not working. Region server will try to update ZK node
during region opening & will fail. Basically all RS with new config can't open any region.
Logically it's equivalent stop every thing and then restart. It's also unclear to me when
a new master starts where it gets RIT info.

2) When hbase.assignment.usezk is ON, a region is set RIT to pending_open before it sends
region open RPC out and master restarts. During restart, how AM processes left over RIT isn't
clear to me. The code seems only process RITs recorded in ZK assignment node.

3) When a region is opened after master receives region transition response from RS, could
we use checkAndPut to update META in order to make sure the region location is the same as
the RS who sends the region transition request to prevent potential double assignment.

4) Inside postOpenDeployTasks, when reportRegionTransition return false we don't offline the
region in RS. If this situation happens, when we open a region which isn't supposed to do
so, the opening has side effects like removing recovered.edits files when recovery mode is
in recover edits mode.

5) A rare race condition that a RS fails to open a region and it reports to master as FAILED_OPEN
but without firstly changing its internal memory state. If master re-assigns the region onto
the same RS, the region open RPC will simply return OPENED and the region will be unassigned

> ZK-less region assignment
> -------------------------
>                 Key: HBASE-11059
>                 URL: https://issues.apache.org/jira/browse/HBASE-11059
>             Project: HBase
>          Issue Type: Improvement
>          Components: master, Region Assignment
>            Reporter: Jimmy Xiang
>            Assignee: Jimmy Xiang
>             Fix For: 0.99.0
>         Attachments: hbase-11059.patch, hbase-11059_v2.1.patch, hbase-11059_v2.2.patch,
hbase-11059_v2.patch, zk-less_am.pdf, zk-less_assignment.png
> It seems that most people don't like region assignment with ZK (HBASE-5487), which causes
many uncertainties. This jira is to support ZK-less region assignment. We need to make sure
this patch doesn't break backward compatibility/rolling upgrade.

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