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Date: Sat, 16 Jan 2016 08:38:39 +0000 (UTC)
From: "Mridul Muralidharan (JIRA)" <jira@apache.org>
To: issues@spark.apache.org
Message-ID: <JIRA.12779594.1425504424000.129447.1452933519871@Atlassian.JIRA>
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Subject: [jira] [Commented] (SPARK-6166) Add config to limit number of
 concurrent outbound connections for shuffle fetch
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    [ https://issues.apache.org/jira/browse/SPARK-6166?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15103065#comment-15103065 ] 

Mridul Muralidharan commented on SPARK-6166:
--------------------------------------------

We actually dont care about number of sockets or connections - but number of block requests which is going out.
That is what we want to put a limit to - think of it as a corresponding limit to number of active requests as we have for number of outstanding bytes in flight.

> Add config to limit number of concurrent outbound connections for shuffle fetch
> -------------------------------------------------------------------------------
>
>                 Key: SPARK-6166
>                 URL: https://issues.apache.org/jira/browse/SPARK-6166
>             Project: Spark
>          Issue Type: Improvement
>          Components: Spark Core
>    Affects Versions: 1.4.0
>            Reporter: Mridul Muralidharan
>            Assignee: Shixiong Zhu
>            Priority: Minor
>
> spark.reducer.maxMbInFlight puts a bound on the in flight data in terms of size.
> But this is not always sufficient : when the number of hosts in the cluster increase, this can lead to very large number of in-bound connections to one more nodes - causing workers to fail under the load.
> I propose we also add a spark.reducer.maxReqsInFlight - which puts a bound on number of outstanding outbound connections.
> This might still cause hotspots in the cluster, but in our tests this has significantly reduced the occurance of worker failures.


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