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https://issues.apache.org/jira/browse/HDFS-6087?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13936395#comment-13936395
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Guo Ruijing commented on HDFS-6087:
-----------------------------------

I think I already resolve Konstantin Shvachko and Tsz Wo Nicholas Sze's 
comments/concerns. I will wait for your new comments/concerns and update it in 
document.

design motivation is:

1) unify HDFS write/append/truncate

2) the design is base of writable snapshot / snapshot restore (This JIRA is not 
created to track snapshot items)

> Unify HDFS write/append/truncate
> --------------------------------
>
>                 Key: HDFS-6087
>                 URL: https://issues.apache.org/jira/browse/HDFS-6087
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs-client
>            Reporter: Guo Ruijing
>         Attachments: HDFS Design Proposal.pdf, HDFS Design Proposal_3_14.pdf
>
>
> In existing implementation, HDFS file can be appended and HDFS block can be 
> reopened for append. This design will introduce complexity including lease 
> recovery. If we design HDFS block as immutable, it will be very simple for 
> append & truncate. The idea is that HDFS block is immutable if the block is 
> committed to namenode. If the block is not committed to namenode, it is HDFS 
> client’s responsibility to re-added with new block ID.



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