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From "Lavkesh Lahngir (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-5123) SQL based RM state store
Date Tue, 24 May 2016 07:04:12 GMT

    [ https://issues.apache.org/jira/browse/YARN-5123?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15297795#comment-15297795

Lavkesh Lahngir commented on YARN-5123:

When RM becomes active, it stores a secret in the credentail table, which is used later to
check the active status. 
In every transaction we hold a shared lock on the credential table. (see getFromTableForShare()
method and http://www.postgresql.org/docs/9.1/static/transaction-iso.html repeatbale read
transaction level). 
If current RM holds the shared lock, the other RM won't be able to modifiy the credentail
table until the transaction is commited or aborted, and if credentail table is modified by
other RM before the transaction has begun, that means second RM has become active. In that
case the current RM will throw FenceExcaption and will go to standby. 
In both cases only one RM will be able to write on the state-store.

> SQL based RM state store
> ------------------------
>                 Key: YARN-5123
>                 URL: https://issues.apache.org/jira/browse/YARN-5123
>             Project: Hadoop YARN
>          Issue Type: New Feature
>    Affects Versions: 2.6.0
>            Reporter: Lavkesh Lahngir
>         Attachments: sqlstatestore.patch
> In our setup,  zookeeper based RM state store didn't work. We ended up implementing our
own SQL based state store. Here is a patch, if anybody else wants to use it. 

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