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Date: Thu, 21 Aug 2008 09:56:44 -0700 (PDT)
From: "Hairong Kuang (JIRA)" <jira@apache.org>
To: core-dev@hadoop.apache.org
Subject: [jira] Commented: (HADOOP-2330) Preallocate transaction log to
 improve namenode transaction logging performance
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    [ https://issues.apache.org/jira/browse/HADOOP-2330?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12624422#action_12624422 ] 

Hairong Kuang commented on HADOOP-2330:
---------------------------------------

Another idea is to set the INVALID_OP code to be 0 and the ADD opcode to be a positive number. Then we do not need to move the file position backwards.

> 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, preallocateTransactionLog2.patch, preallocateTransactionLog3.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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