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Date: Tue, 2 Nov 2010 15:08:30 -0400 (EDT)
From: "stack (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Subject: [jira] Commented: (HDFS-895) Allow hflush/sync to occur in parallel
 with new writes to the file
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    [ https://issues.apache.org/jira/browse/HDFS-895?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12927552#action_12927552 ] 

stack commented on HDFS-895:
----------------------------

@Hairong He's out for a few days (wandering temples in foreign lands)

> Allow hflush/sync to occur in parallel with new writes to the file
> ------------------------------------------------------------------
>
>                 Key: HDFS-895
>                 URL: https://issues.apache.org/jira/browse/HDFS-895
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs client
>    Affects Versions: 0.22.0
>            Reporter: dhruba borthakur
>            Assignee: Todd Lipcon
>             Fix For: 0.22.0
>
>         Attachments: hdfs-895-0.20-append.txt, hdfs-895-20.txt, hdfs-895-review.txt, hdfs-895-trunk.txt, hdfs-895.txt, hdfs-895.txt
>
>
> In the current trunk, the HDFS client methods writeChunk() and hflush./sync are syncronized. This means that if a hflush/sync is in progress, an applicationn cannot write data to the HDFS client buffer. This reduces the write throughput of the transaction log in HBase. 
> The hflush/sync should allow new writes to happen to the HDFS client even when a hflush/sync is in progress. It can record the seqno of the message for which it should receice the ack, indicate to the DataStream thread to star flushing those messages, exit the synchronized section  and just wai for that ack to arrive.

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