hadoop-common-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Suresh Srinivas (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4584) Slow generation of blockReport at DataNode causes delay of sending heartbeat to NameNode
Date Thu, 26 Mar 2009 20:48:50 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4584?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12689645#action_12689645
] 

Suresh Srinivas commented on HADOOP-4584:
-----------------------------------------

Here is why holding FSDataset lock is not required:
# When reconciling, the difference flagged by the scanner is only a hint to check the. The
actual state of the block on disk and volumeMap is used to decide if indeed the difference
still exists. This takes care of the following conditions:
#* Scanner finds a block but it has been deleted after it was found
#* Scanner does not find a block that has been added during scan
# DirectoryScanner might not find differences for the blocks that got added or deleted, while
it compares the block report from memory and the disk. These differences will be found in
the next iteration of the scanner.

I will add this information to the document as well.


> Slow generation of blockReport at DataNode causes delay of sending heartbeat to NameNode
> ----------------------------------------------------------------------------------------
>
>                 Key: HADOOP-4584
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4584
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: dfs
>            Reporter: Hairong Kuang
>            Assignee: Suresh Srinivas
>             Fix For: 0.20.0
>
>         Attachments: 4584.brthread.2.patch, 4584.brthread.3.patch, 4584.brthread.3.patch,
4584.brthread.3.patch, 4584.brthread.3.patch, 4584.brthread.3.patch, 4584.hbthread.patch,
4584.patch, 4584.patch, 4584.patch, 4584.patch, 4584.patch, 4584.patch, Design.pdf
>
>
> sometimes due to disk or some other problems, datanode takes minutes or tens of minutes
to generate a block report. It causes the datanode not able to send heartbeat to NameNode
every 3 seconds. In the worst case, it makes NameNode to detect a lost heartbeat and wrongly
decide that the datanode is dead.
> It would be nice to have two threads instead. One thread is for scanning data directories
and generating block report, and executes the requests sent by NameNode; Another thread is
for sending heartbeats, block reports, and picking up the requests from NameNode. By having
these two threads, the sending of heartbeats will not get delayed by any slow block report
or slow execution of NameNode requests.

-- 
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.


Mime
View raw message