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From "Flavio Junqueira (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3077) Quorum-based protocol for reading and writing edit logs
Date Fri, 30 Mar 2012 23:07:26 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13242834#comment-13242834
] 

Flavio Junqueira commented on HDFS-3077:
----------------------------------------

bq. True, though BK takes effort to interleave all of the ledgers into a single sequential
stream, while writing an index file to allow de-interleaving upon read.

We have done this interleaving originally because the performance was affected even with just
a handful of log files (ledgers). The solution we have currently apply to a few or tens of
thousands of ledgers. 

If you're concerned about read performance, we have not observed any important reduction.
About de-interleaving, we don't rearrange it or anything, if that's what you have in mind.
       
                
> 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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