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Date: Wed, 13 Jun 2012 02:59:43 +0000 (UTC)
From: "Zhihong Ted Yu (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
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Subject: [jira] [Commented] (HDFS-1783) Ability for HDFS client to write
 replicas in parallel
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    [ https://issues.apache.org/jira/browse/HDFS-1783?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13294094#comment-13294094 ] 

Zhihong Ted Yu commented on HDFS-1783:
--------------------------------------

{code}
  public FSDataOutputStream create(Path f,
      FsPermission permission,
      EnumSet<CreateFlag> flags,
      int bufferSize,
      short replication,
      long blockSize,
      Progressable progress) throws IOException {
{code}
The above method only respects CreateFlag.OVERWRITE:
{code}
    return create(f, permission, flags.contains(CreateFlag.OVERWRITE), bufferSize, replication, blockSize, progress);
{code}
This method calls append if CreateFlag.APPEND is specified:
{code}
  protected FSDataOutputStream primitiveCreate(Path f,
     FsPermission absolutePermission, EnumSet<CreateFlag> flag, int bufferSize,
     short replication, long blockSize, Progressable progress,
     int bytesPerChecksum) throws IOException {
{code}

                
> Ability for HDFS client to write replicas in parallel
> -----------------------------------------------------
>
>                 Key: HDFS-1783
>                 URL: https://issues.apache.org/jira/browse/HDFS-1783
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs client
>            Reporter: dhruba borthakur
>            Assignee: Lars Hofhansl
>         Attachments: HDFS-1783-trunk-v2.patch, HDFS-1783-trunk-v3.patch, HDFS-1783-trunk-v4.patch, HDFS-1783-trunk-v5.patch, HDFS-1783-trunk.patch
>
>
> The current implementation of HDFS pipelines the writes to the three replicas. This introduces some latency for realtime latency sensitive applications. An alternate implementation that allows the client to write all replicas in parallel gives much better response times to these applications. 

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