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From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-2330) Preallocate transaction log to improve namenode transaction logging performance
Date Wed, 20 Aug 2008 17:56:47 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-2330?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12624069#action_12624069
] 

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

I think setting a channel's position is the same as seeking. So these two lines in your patch
are equivalent:
fc.position(fc.size());
rp.seek(fc.size());

Did you mean that fc.position(size) is not reliable?

> 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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