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From "dud (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HADOOP-14411) HDFS architecture documentation describes outdated placement policy
Date Thu, 11 May 2017 10:40:04 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-14411?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

dud updated HADOOP-14411:
-------------------------
    Description: 
Hello

I've noticed inconsistencies in the default block placement policy between what one can read
on several websites and what is stated in the [official documentation|https://git-wip-us.apache.org/repos/asf?p=hadoop.git;a=blob;f=hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HdfsDesign.md;h=bda53a9c77b41308eef3abf5b478158b2ea03be0;hb=HEAD#l105].

After digging, I've found out that the proper default placement policy is :
{code}
 * The replica placement strategy is that if the writer is on a datanode,
 * the 1st replica is placed on the local machine, 
 * otherwise a random datanode. The 2nd replica is placed on a datanode
 * that is on a different rack. The 3rd replica is placed on a datanode
 * which is on a different node of the rack as the second replica.
 {code}

[source|https://git-wip-us.apache.org/repos/asf?p=hadoop.git;a=blob;f=hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockPlacementPolicyDefault.java#l45]

HADOOP-5734 has been opened regarding this mistake several years ago and has eventually been
merged but unfortunately this fix has been overwritten by [~tucu00]  in [SVN commit|https://svn.apache.org/viewvc?view=revision&revision=1425527].

dud

  was:
Hello

I've noticed inconsistencies in the default block placement policy between what one can read
on several websites and what is stated in the official documentation.

After digging, I've found out that the proper default placement policy is :
{code}
 * The replica placement strategy is that if the writer is on a datanode,
 * the 1st replica is placed on the local machine, 
 * otherwise a random datanode. The 2nd replica is placed on a datanode
 * that is on a different rack. The 3rd replica is placed on a datanode
 * which is on a different node of the rack as the second replica.
 {code}

[source|https://git-wip-us.apache.org/repos/asf?p=hadoop.git;a=blob;f=hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockPlacementPolicyDefault.java#l45]

HADOOP-5734 has been opened regarding this mistake several years ago and has eventually been
merged but unfortunately this fix has been overwritten by [~tucu00]  in [SVN commit|https://svn.apache.org/viewvc?view=revision&revision=1425527].

dud


> HDFS architecture documentation describes outdated placement policy
> -------------------------------------------------------------------
>
>                 Key: HADOOP-14411
>                 URL: https://issues.apache.org/jira/browse/HADOOP-14411
>             Project: Hadoop Common
>          Issue Type: Improvement
>            Reporter: dud
>            Priority: Minor
>              Labels: documentation
>
> Hello
> I've noticed inconsistencies in the default block placement policy between what one can
read on several websites and what is stated in the [official documentation|https://git-wip-us.apache.org/repos/asf?p=hadoop.git;a=blob;f=hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HdfsDesign.md;h=bda53a9c77b41308eef3abf5b478158b2ea03be0;hb=HEAD#l105].
> After digging, I've found out that the proper default placement policy is :
> {code}
>  * The replica placement strategy is that if the writer is on a datanode,
>  * the 1st replica is placed on the local machine, 
>  * otherwise a random datanode. The 2nd replica is placed on a datanode
>  * that is on a different rack. The 3rd replica is placed on a datanode
>  * which is on a different node of the rack as the second replica.
>  {code}
> [source|https://git-wip-us.apache.org/repos/asf?p=hadoop.git;a=blob;f=hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockPlacementPolicyDefault.java#l45]
> HADOOP-5734 has been opened regarding this mistake several years ago and has eventually
been merged but unfortunately this fix has been overwritten by [~tucu00]  in [SVN commit|https://svn.apache.org/viewvc?view=revision&revision=1425527].
> dud



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