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From "Todd Lipcon (Updated) (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-2379) 0.20: Allow block reports to proceed without holding FSDataset lock
Date Tue, 11 Oct 2011 19:49:12 GMT

     [ https://issues.apache.org/jira/browse/HDFS-2379?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Todd Lipcon updated HDFS-2379:
------------------------------

    Attachment: hdfs-2379.txt

Updated patch. I ran a manual test with 4 datanodes where I inserted a few hundred blocks,
then on one of the datanodes did "rm blk_*" in one of the data directories. I had configured
the block report interval to 10 seconds, and on the next block report, the NN counted these
blocks as under-replicated. After a minute or two, everything was fully replicated again.
                
> 0.20: Allow block reports to proceed without holding FSDataset lock
> -------------------------------------------------------------------
>
>                 Key: HDFS-2379
>                 URL: https://issues.apache.org/jira/browse/HDFS-2379
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: data-node
>    Affects Versions: 0.20.206.0
>            Reporter: Todd Lipcon
>            Priority: Critical
>         Attachments: hdfs-2379.txt, hdfs-2379.txt, hdfs-2379.txt, hdfs-2379.txt, hdfs-2379.txt
>
>
> As disks are getting larger and more plentiful, we're seeing DNs with multiple millions
of blocks on a single machine. When page cache space is tight, block reports can take multiple
minutes to generate. Currently, during the scanning of the data directories to generate a
report, the FSVolumeSet lock is held. This causes writes and reads to block, timeout, etc,
causing big problems especially for clients like HBase.
> This JIRA is to explore some of the ideas originally discussed in HADOOP-4584 for the
0.20.20x series.

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