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Posted to common-dev@hadoop.apache.org by "Benjamin Reed (JIRA)" <ji...@apache.org> on 2008/07/17 22:41:31 UTC

[jira] Commented: (HADOOP-2330) Preallocate transaction log to improve namenode transaction logging performance

    [ https://issues.apache.org/jira/browse/HADOOP-2330?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12614526#action_12614526 ] 

Benjamin Reed commented on HADOOP-2330:
---------------------------------------

You also need to change fc.force(true);   to fc.force(false); otherwise the preallocation isn't buying you much. You need both the preallocation and fc.force(false) to avoid the sync. Note: fc.force(false) means only sync the data not the metadata (timestamps in this case).  

> Preallocate transaction log to improve namenode transaction logging performance
> -------------------------------------------------------------------------------
>
>                 Key: HADOOP-2330
>                 URL: https://issues.apache.org/jira/browse/HADOOP-2330
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: dfs
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>         Attachments: preallocateTransactionLog.patch, preallocateTransactionLog.patch
>
>
> In the current implementation, the transaction log is opened in "append" mode and every new transaction is written to the end of the log. This means that new blocks get allocated to the edits file frequently.
> It is worth measuring the performance improvement when big chunks of the transaction log are allocated up front. Adding new transactions do not cause frequent block allocations for the edits log.

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