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From "Flavio Paiva Junqueira (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-5188) Modifications to enable multiple types of logging
Date Fri, 08 May 2009 21:46:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-5188?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12707535#action_12707535

Flavio Paiva Junqueira commented on HADOOP-5188:

It is perhaps not clear what problem point number 3 of the concrete tasks is trying to solve.
If I understand it correctly, there is an opcode (OP_JSPOOL_START) that the backup node uses
to mark an edits stream and determine the last synchronization point. I believe the idea is
to leverage this mechanism to close one ledger and create another ledger when using BookKeeper.
In general, this mechanism flags to any log device where synchronization points are, and let
each device handle accordingly. The important property here is that all devices will observe
the same synchronization points and in the same positions. 

One problem with the implementation of this marking mechanism is that it is a little obscure
in the code, so you need to know that it is there. What I believe the design document is proposing
is to add an interface method that forces a developer implementing the adapter for some new
log device to get a error at compile time if it doesn't implement such a method. For the streams
that do not support such markers, the method call would be a simple no-op. Also, an implementation
of the method isOperationSupported() might be unnecessary if we do have such an interface

Comments or clarifications?

> Modifications to enable multiple types of logging 
> --------------------------------------------------
>                 Key: HADOOP-5188
>                 URL: https://issues.apache.org/jira/browse/HADOOP-5188
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: dfs
>    Affects Versions: 0.19.0
>            Reporter: Luca Telloli
>         Attachments: HADOOP-5188.patch, HADOOP-5188.pdf

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