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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Created: (HDFS-822) Appends to already-finalized blocks can rename across volumes
Date Thu, 10 Dec 2009 00:50:18 GMT
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

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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