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From "Aaron T. Myers (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3077) Quorum-based protocol for reading and writing edit logs
Date Thu, 19 Jul 2012 23:05:35 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13418763#comment-13418763
] 

Aaron T. Myers commented on HDFS-3077:
--------------------------------------

The latest patch looks good to me. Just a few small nits. +1 to commit to a branch once these
are addressed. Please also file follow-up JIRAs for the TODOs that are deliberately being
left in this patch.

# Style nit - there are a few places where you unnecessarily put method arguments on separate
lines, even if the line isn't approaching 80 chars, e.g.:
{code}
+      public GetEditLogManifestResponseProto call() throws IOException {
+        return getProxy().getEditLogManifest(
+            journalId,
+            fromTxnId);
+      }
{code}
# Instead of System#nanoTime you should use Time#monotonicNow.
# s/Journal service/Journal Node/g: "This class is used by the lagging Journal service to
retrieve edit file from another Journal service for sync up."
# Some odd formatting:
{code}
+      response
+          .sendError(HttpServletResponse.SC_FORBIDDEN,
+              "Only Namenode and another Journal service may access this servlet");
{code}
                
> 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
>         Attachments: hdfs-3077-partial.txt, hdfs-3077.txt, hdfs-3077.txt, hdfs-3077.txt,
hdfs-3077.txt, hdfs-3077.txt, hdfs-3077.txt, qjournal-design.pdf, qjournal-design.pdf
>
>
> 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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