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MapReduce, mail # user - Shuffle phase replication factor


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RE: Shuffle phase replication factor
John Lilley 2013-05-22, 14:57
Ummmm, is that also the limit for the number of simultaneous connections?  In general, one does not need a 1:1 map between threads and connections.
If this is the connection limit, does it imply  that the client or server side aggressively disconnects after a transfer?
What happens to the pending/failing connection attempts that exceed the limit?
Thanks!
john

From: Rahul Bhattacharjee [mailto:[EMAIL PROTECTED]]
Sent: Wednesday, May 22, 2013 8:52 AM
To: [EMAIL PROTECTED]
Subject: Re: Shuffle phase replication factor

There are properties/configuration to control the no. of copying threads for copy.
tasktracker.http.threads=40
Thanks,
Rahul

On Wed, May 22, 2013 at 8:16 PM, John Lilley <[EMAIL PROTECTED]<mailto:[EMAIL PROTECTED]>> wrote:
This brings up another nagging question I’ve had for some time.  Between HDFS and shuffle, there seems to be the potential for “every node connecting to every other node” via TCP.  Are there explicit mechanisms in place to manage or limit simultaneous connections?  Is the protocol simply robust enough to allow a server-side to disconnect at any time to free up slots and the client-side will retry the request?
Thanks
john

From: Shahab Yunus [mailto:[EMAIL PROTECTED]<mailto:[EMAIL PROTECTED]>]
Sent: Wednesday, May 22, 2013 8:38 AM

To: [EMAIL PROTECTED]<mailto:[EMAIL PROTECTED]>
Subject: Re: Shuffle phase replication factor

As mentioned by Bertrand, Hadoop, The Definitive Guide, is well... really definitive :) place to start. It is pretty thorough for starts and once you are gone through it, the code will start making more sense too.

Regards,
Shahab

On Wed, May 22, 2013 at 10:33 AM, John Lilley <[EMAIL PROTECTED]<mailto:[EMAIL PROTECTED]>> wrote:
Oh I see.  Does this mean there is another service and TCP listen port for this purpose?
Thanks for your indulgence… I would really like to read more about this without bothering the group but not sure where to start to learn these internals other than the code.
john

From: Kai Voigt [mailto:[EMAIL PROTECTED]<mailto:[EMAIL PROTECTED]>]
Sent: Tuesday, May 21, 2013 12:59 PM
To: [EMAIL PROTECTED]<mailto:[EMAIL PROTECTED]>
Subject: Re: Shuffle phase replication factor

The map output doesn't get written to HDFS. The map task writes its output to its local disk, the reduce tasks will pull the data through HTTP for further processing.

Am 21.05.2013 um 19:57 schrieb John Lilley <[EMAIL PROTECTED]<mailto:[EMAIL PROTECTED]>>:

When MapReduce enters “shuffle” to partition the tuples, I am assuming that it writes intermediate data to HDFS.  What replication factor is used for those temporary files?
john
--
Kai Voigt
[EMAIL PROTECTED]<mailto:[EMAIL PROTECTED]>