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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, 18 Oct 2011 03:02:15 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

bq. getBlockReport() javadoc is unnecessary
bq. minor: "Request that an block report" -> "Request that a "
bq. Make asyncBlockReport final.
bq. (!requested || scan != null) is better readable as !(requested && scan == null)

bq. Indentation of String metaPart = ... could be better
Fixed - also added a constant for METADATA_EXTENSION_LENGTH instead of the bare constant 5.

bq. 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
Answered this in the comment above. It's now removed.

bq. Why are you sleeping for 2 seconds on catching Throwable?
Added this comment:
+            // Avoid busy-looping in the case that we have entered some invalid
+            // state -- don't want to flood the error log with exceptions.
(my experience in other parts of the DN was that these types of busy loops caused big problems)

bq. Optional - This might be a good time to move some of the block reported code into a separate
method, outside offerService().
I agree it would be a nice cleanup, but wanted to keep this change minimal.

> 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:
>            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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