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From "Suresh Srinivas (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3092) Enable journal protocol based editlog streaming for standby namenode
Date Tue, 03 Apr 2012 17:28:27 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3092?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13245523#comment-13245523

Suresh Srinivas commented on HDFS-3092:

bq. When you say three JDs, that's the degree of replication, right? When I said multiple
logs, I was referring to multiple namenodes writing to different logs, as with federation.
Right, three JDs for degree of replication. However, I do understand multiple logs - that
is a log per namespace. For every namespace, in federation, active and standby namenode +
additional JD is needed.

bq. I think my confusion here is that you require a quorum to be able to acknowledge the operation,
but in reality you try to write to everyone. If you can't write to everyone, then you induce
a view change (change to JournalList). Is this right?
Yes. In the first cut we write to all the JDs that are active. At least quorum should be written.
This can be improved in the future by waiting for only Quorum JDs.
> Enable journal protocol based editlog streaming for standby namenode
> --------------------------------------------------------------------
>                 Key: HDFS-3092
>                 URL: https://issues.apache.org/jira/browse/HDFS-3092
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: ha, name-node
>    Affects Versions: 0.24.0, 0.23.3
>            Reporter: Suresh Srinivas
>            Assignee: Suresh Srinivas
>         Attachments: MultipleSharedJournals.pdf
> Currently standby namenode relies on reading shared editlogs to stay current with the
active namenode, for namespace changes. BackupNode used streaming edits from active namenode
for doing the same. This jira is to explore using journal protocol based editlog streams for
the standby namenode. A daemon in standby will get the editlogs from the active and write
it to local edits. To begin with, the existing standby mechanism of reading from a file, will
continue to be used, instead of from shared edits, from the local edits.

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