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From "Sergey Shelukhin (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5487) Generic framework for Master-coordinated tasks
Date Wed, 09 Oct 2013 00:33:44 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5487?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13789874#comment-13789874

Sergey Shelukhin commented on HBASE-5487:

bq. We've tried putting state into zk.  That failed.  I really don't want to put a whole bunch
of new code into hbase that does almost exactly the same thing as we currently have.  It's
going to fail.
As I said I don't think that is true. Our problem is not state being in ZK; it is that the
state is in multiple places in ZK itself for different parts of the same region's state, plus
some state in master to reconcile these, plus some state that is not in ZK but only in master,
plus also meta.
I.e. not the split between ZK and master but split logical state within both and between them.
bq.  Then you need a local cache if you want to make this performant at all (That's how we
got to the current state).
Our current state is not local cache, it's a bunch of actual state...

I am not yet sure how bad ZK-master split brain problem will be if ZK has entire truth, let
me think about it.
When you say no split-brain inside master, do you mean master will host the meta and do all
reads and writes to meta with no local intermediate state in memory?

> Generic framework for Master-coordinated tasks
> ----------------------------------------------
>                 Key: HBASE-5487
>                 URL: https://issues.apache.org/jira/browse/HBASE-5487
>             Project: HBase
>          Issue Type: New Feature
>          Components: master, regionserver, Zookeeper
>    Affects Versions: 0.94.0
>            Reporter: Mubarak Seyed
>            Priority: Critical
>         Attachments: Region management in Master.pdf
> Need a framework to execute master-coordinated tasks in a fault-tolerant manner. 
> Master-coordinated tasks such as online-scheme change and delete-range (deleting region(s)
based on start/end key) can make use of this framework.
> The advantages of framework are
> 1. Eliminate repeated code in Master, ZooKeeper tracker and Region-server for master-coordinated
> 2. Ability to abstract the common functions across Master -> ZK and RS -> ZK
> 3. Easy to plugin new master-coordinated tasks without adding code to core components

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