Zsolt Venczel updated HDFS-13573:
    Attachment: HDFS-13573.02.patch

> Javadoc for BlockPlacementPolicyDefault is inaccurate
> -----------------------------------------------------
>                 Key: HDFS-13573
>                 URL: https://issues.apache.org/jira/browse/HDFS-13573
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 3.1.0
>            Reporter: Yiqun Lin
>            Assignee: Zsolt Venczel
>            Priority: Trivial
>         Attachments: HDFS-13573.01.patch, HDFS-13573.02.patch
> Current rule of default block placement policy:
> {quote}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.
> {quote}
> *if the writer is on a datanode, the 1st replica is placed on the local 
> machine*, actually this can be decided by the hdfs client. The client can 
> pass {{CreateFlag#NO_LOCAL_WRITE}} that request to not put a block replica on 
> the local datanode. But subsequent replicas will still follow default block 
> placement policy.

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