hadoop-hdfs-issues mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-767) Job failure due to BlockMissingException
Date Thu, 12 Nov 2009 21:32:39 GMT

    [ https://issues.apache.org/jira/browse/HDFS-767?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12777217#action_12777217
] 

Todd Lipcon commented on HDFS-767:
----------------------------------

Hi Ning,

The formula seems reasonable but slightly more complicated than necessary. Why not simply
use truncated binary exponential backoff like ethernet? http://en.wikipedia.org/wiki/Truncated_binary_exponential_backoff
- this formula is well known and proven to be effective for similar situations.

> Job failure due to BlockMissingException
> ----------------------------------------
>
>                 Key: HDFS-767
>                 URL: https://issues.apache.org/jira/browse/HDFS-767
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Ning Zhang
>
> If a block is request by too many mappers/reducers (say, 3000) at the same time, a BlockMissingException
is thrown because it exceeds the upper limit (I think 256 by default) of number of threads
accessing the same block at the same time. The DFSClient wil catch that exception and retry
3 times after waiting for 3 seconds. Since the wait time is a fixed value, a lot of clients
will retry at about the same time and a large portion of them get another failure. After 3
retries, there are about 256*4 = 1024 clients got the block. If the number of clients are
more than that, the job will fail. 

-- 
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