[
https://issues.apache.org/jira/browse/MAPREDUCE-1800?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12869734#action_12869734
]
Ramkumar Vadali commented on MAPREDUCE-1800:
--------------------------------------------
>From my understanding, a map output fetch is a HTTP GET. I agree that
>TCP-level network errors are not good indicators to use for blacklisting since
>it is not possible to distinguish between a server-side error and a network
>error. But HTTP-level errors, especially HTTP 5xx errors (used for server-side
>errors) should be used for blacklisting. Disk failures that prevent the HTTP
>server from reading a file would fall in this category. It is possible that
>such errors could be detected by Map failures, but a HTTP 5xx error is a
>fairly reliable indicator of error.
So in my opinion we should retain the blacklisting, but make it smarter to use
HTTP-level error information.
> using map output fetch failures to blacklist nodes is problematic
> -----------------------------------------------------------------
>
> Key: MAPREDUCE-1800
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-1800
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Reporter: Joydeep Sen Sarma
>
> If a mapper and a reducer cannot communicate, then either party could be at
> fault. The current hadoop protocol allows reducers to declare nodes running
> the mapper as being at fault. When sufficient number of reducers do so - then
> the map node can be blacklisted.
> In cases where networking problems cause substantial degradation in
> communication across sets of nodes - then large number of nodes can become
> blacklisted as a result of this protocol. The blacklisting is often wrong
> (reducers on the smaller side of the network partition can collectively cause
> nodes on the larger network partitioned to be blacklisted) and
> counterproductive (rerunning maps puts further load on the (already) maxed
> out network links).
> We should revisit how we can better identify nodes with genuine network
> problems (and what role, if any, map-output fetch failures have in this).
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
