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From "Todd Lipcon (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3077) Quorum-based protocol for reading and writing edit logs
Date Wed, 14 Mar 2012 19:26:39 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13229529#comment-13229529
] 

Todd Lipcon commented on HDFS-3077:
-----------------------------------

bq. Sequencing writes between different writers is the hard part. BookKeeper seems to do this
by using ZK to enforce mutual exclusion, which means at its heart it too relies on a consensus
protocol to cope with these tricky failure cases. This makes it a very legitimate point in
the design space, but one that shares plenty with the proposal here.

Yep -- rather than fully implement ZAB, my initial implementation will also rely on ZK for
writer sequencing. If we want to use this outside the context of ZK (for example with a different
failure detector for the NNs) we could move on to implement the epoch-sequencing bit of ZAB.
                
> Quorum-based protocol for reading and writing edit logs
> -------------------------------------------------------
>
>                 Key: HDFS-3077
>                 URL: https://issues.apache.org/jira/browse/HDFS-3077
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: ha, name-node
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>
> Currently, one of the weak points of the HA design is that it relies on shared storage
such as an NFS filer for the shared edit log. One alternative that has been proposed is to
depend on BookKeeper, a ZooKeeper subproject which provides a highly available replicated
edit log on commodity hardware. This JIRA is to implement another alternative, based on a
quorum commit protocol, integrated more tightly in HDFS and with the requirements driven only
by HDFS's needs rather than more generic use cases. More details to follow.

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