[jira] Updated: (HDFS-822) Appends to already-finalized blocks can rename across volumes

["Hairong Kuang (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HDFS-822?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Hairong Kuang updated HDFS-822:
-------------------------------

         Priority: Blocker  (was: Major)
    Fix Version/s: 0.22.0
                   0.21.0
         Assignee: Hairong Kuang

This is a valid point. Let's get it fixed in 0.21.

> Appends to already-finalized blocks can rename across volumes
> -------------------------------------------------------------
>
>                 Key: HDFS-822
>                 URL: https://issues.apache.org/jira/browse/HDFS-822
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: data-node
>    Affects Versions: 0.21.0, 0.22.0
>            Reporter: Todd Lipcon
>            Assignee: Hairong Kuang
>            Priority: Blocker
>             Fix For: 0.21.0, 0.22.0
>
>
> This is a performance thing. As I understand the code in FSDataset.append, if the block is already finalized, it needs to move it into the RBW directory so it can go back into a "being written" state. This is done using volumes.getNextVolume without preference to the volume that the block currently exists on. It seems to me that this could cause a lot of slow cross-volume copies on applications that periodically append/close/append/close a file. Instead, getNextVolume could provide an alternate form that gives preference to a particular volume, so the rename stays on the same disk.

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