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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-1108) Log newly allocated blocks
Date Tue, 23 Aug 2011 18:42:29 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1108?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13089658#comment-13089658
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Konstantin Shvachko commented on HDFS-1108:
-------------------------------------------

bq. We currently log addBlocks but don't call logSync, assumedly to save on performance. 

I think this is the right implementation for this functionality. We will always have consistent
state in memory and rely on batching to do the actual sync, which is common.

bq. I'll add logSync for now, and if people find a regression we can add a config to disable
it.

This should be similar to how we treat setTime(). Please don't add logSync on every addBlock().

Just to make sure its not misread, I am -1 on this.
Regression of this particular change can be noticed only right now. I am also skeptical about
introducing more config variables.

> Log newly allocated blocks
> --------------------------
>
>                 Key: HDFS-1108
>                 URL: https://issues.apache.org/jira/browse/HDFS-1108
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: name-node
>            Reporter: dhruba borthakur
>            Assignee: Todd Lipcon
>             Fix For: HA branch (HDFS-1623)
>
>         Attachments: HDFS-1108.patch, hdfs-1108-habranch.txt, hdfs-1108.txt
>
>
> The current HDFS design says that newly allocated blocks for a file are not persisted
in the NN transaction log when the block is allocated. Instead, a hflush() or a close() on
the file persists the blocks into the transaction log. It would be nice if we can immediately
persist newly allocated blocks (as soon as they are allocated) for specific files.

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