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From "Suresh Srinivas (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2379) 0.20: Allow block reports to proceed without holding FSDataset lock
Date Tue, 11 Oct 2011 21:31:12 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2379?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13125402#comment-13125402
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Suresh Srinivas commented on HDFS-2379:
---------------------------------------

FSDatasetInterface.java
# getBlockReport() javadoc is unnecessary.
# minor: "Request that an block report" -> "Request that a "
# retrieveAsyncBlockReport - javadoc is not very clear. Also change to javadoc of getBlockReport()
is not necessary.

FSDataset.java
# Indentation of {{String metaPart = ...}} could be better.
# Why do you want to deprecate #getBlockInfo()? If you have a valid reason, can you please
add information on the new method/mechanism that should be used instead of the deprecated
method.
# Make asyncBlockReport final.
# Why do you choose to notifyAll when requested is set to true, but not when scan is set to
null or requested is set to false?
# AsyncBlockReport#run - Why are you sleeping for 2 seconds on catching Throwable?
#  (!requested || scan != null) is better readable as !(requested && scan == null)

Datanode.java
# Optional - This might be a good time to move some of the block reported code into a separate
method, outside offerService().


                
> 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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