[jira] [Commented] (HDFS-7943) Append cannot handle the last block with length greater than the preferred block size

["Jing Zhao (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-7943?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14365720#comment-14365720 ] 

Jing Zhao commented on HDFS-7943:
---------------------------------

We have two options to fix:
# Change append to support blocks with size greater than the preferred block size. Specifically, we can update the logic of {{BlockManager#convertLastBlockToUnderConstruction}}: if the last block size is greater than or equal to the preferred size, the client should write to a new block. Since the same function is also used by truncate, the new logic should also support the scenario that data is truncated from such block.
# Or we can add a new restriction to concat: the source file's preferred block size cannot be greater than the target. This fix is simpler and keeps the semantic that the preferred block size is the upper limit of a file's blocks.

> Append cannot handle the last block with length greater than the preferred block size
> -------------------------------------------------------------------------------------
>
>                 Key: HDFS-7943
>                 URL: https://issues.apache.org/jira/browse/HDFS-7943
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 2.7.0
>            Reporter: Jing Zhao
>            Assignee: Jing Zhao
>            Priority: Blocker
>
> In HDFS-3689, we remove the restriction from concat that all the source files should have the same preferred block size with the target file. This can cause a file to contain blocks with size larger than its preferred block size.
> If such block happens to be the last block of a file, and later we append data to the file without the {{CreateFlag.NEW_BLOCK}} flag (i.e., appending data to the last block), looks like the current client code will keep writing to the last block and never allocate a new block.



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