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Date: Thu, 14 Dec 2006 17:15:24 -0800 (PST)
From: "Konstantin Shvachko (JIRA)" <jira@apache.org>
To: hadoop-dev@lucene.apache.org
Subject: [jira] Commented: (HADOOP-227) Namespace check pointing is not
 performed until the namenode restarts.
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    [ http://issues.apache.org/jira/browse/HADOOP-227?page=comments#action_12458650 ] 
            
Konstantin Shvachko commented on HADOOP-227:
--------------------------------------------

>    * fs.checkpoint.period : Time (in seconds) between two checkpoints.
This is the maximal time between the checkpoints, right?

We should introduce new NamenodeProtocol for primary to secondary name-node communication.

I'd go in the other direction: the primary node checks the edits log size each time it adds an entry.
When it reaches the checkpoint.size or if the checkpoint was not done longer than checkpoint.period
the primary rolls the edits log and sends a command to the secondary node to create a new checkpoint.

I think we should think about supporting multiple secondary nodes at least at the design stage.
In that case we will need to further propagate the checkpoints.
Or do we just write the latest image into hdfs?


> Namespace check pointing is not performed until the namenode restarts.
> ----------------------------------------------------------------------
>
>                 Key: HADOOP-227
>                 URL: http://issues.apache.org/jira/browse/HADOOP-227
>             Project: Hadoop
>          Issue Type: Bug
>          Components: dfs
>    Affects Versions: 0.2.0
>            Reporter: Konstantin Shvachko
>         Assigned To: dhruba borthakur
>         Attachments: patch-async-checkpoints-0.9.0, patch-async-checkpoints-0.9.0, patch-async-checkpoints-0.9.0
>
>
> In current implementation when the name node starts, it reads its image file, then
> the edits file, and then saves the updated image back into the image file.
> The image file is never updated after that.
> In order to provide the system reliability reliability the namespace information should
> be check pointed periodically, and the edits file should be kept relatively small.

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