Hi Devaraj,
The issue Amir brings up has to do with the Testcase scenario.
We are trying to determine if this is a Design issue with the getMoreSplits
() method in CombineFileInputFormat class or if the testcase needs
modification.
Like I mentioned in my earlier note, the observation we made while
debugging this issue is that the order by which the racksToBlocks HashMap
gets populated seems to matter. From the comments by Robert Evans and you,
it appears by design that the order should not matter.
Amir's point is - The reason order happens to play a role here is that as
soon as all the blocks are accounted for, getMoreSplits() stops iterating
through the racks, and depending upon which rack(s) each block is
replicated on, and depending upon when each rack is processed in the loop
within getMoreSplits(), one can end up with different split counts, and as
a result fail the testcase in some situations.
Specifically for this testcase, there are 3 racks that are simulated where
each of these 3 racks have a datanode each. Datanode 1 has replicas of all
the blocks of all the 3 files (file1, file2, and file3) while Datanode 2
has all the blocks of files file2 and file 3 and Datanode 3 has all the
blocks of only file3. As soon as Rack 1 is processed, getMoreSplits() exits
with a split count of the number of times it stays in this loop. So in this
scenario, if Rack1 gets processed last, one will end up with a split count
of 3. If Rack1 gets processed in the beginning, split count will be 1. The
testcase is expecting a return value of 3 but can get a 1 or 2 depending on
when it gets processed.
Hope this clarifies things a bit.
Regards,
Kumar
Kumar Ravi
IBM Linux Technology Center
Austin, TX
Tel.: (512)286-8179
From: Devaraj Das <d...@hortonworks.com>
To: common-dev@hadoop.apache.org
Cc: Jeffrey J Heroux/Poughkeepsie/IBM@IBMUS, John
Williams/Austin/IBM@IBMUS
Date: 03/22/2012 04:41 PM
Subject: Re: Question about Hadoop-8192 and rackToBlocks ordering
On Mar 22, 2012, at 11:45 AM, Amir Sanjar wrote:
> Thanks for the reply Robert,
> However I believe the main design issue is:
> If there is a rack ( listed in rackToBlock hashMap) that contains all the
> blocks (stored in blockToNode hashMap), regardless of the order, the
split
> operation terminates after the rack gets processed, That means remaining
> racks ( listed in rackToBlock hashMap) will not get processed . For
more
> details look at file CombineFileInputFormat.JAVA, method getMoreSplits(),
> while loop starting at line 344.
>
I haven't looked at the code much yet. But trying to understand your
question - what issue are you trying to bring out? Is it overloading one
task with too much input (there is a min/max limit on that one though)?
> Best Regards
> Amir Sanjar
>
> Linux System Management Architect and Lead
> IBM Senior Software Engineer
> Phone# 512-286-8393
> Fax# 512-838-8858
>
>
>
>
>
> From: Robert Evans <ev...@yahoo-inc.com>
> To: "common-dev@hadoop.apache.org" <common-dev@hadoop.apache.org>
> Date: 03/22/2012 11:57 AM
> Subject: Re: Question about Hadoop-8192 and rackToBlocks
> ordering
>
>
>
> If it really is the ordering of the hash map I would say no it should
not,
> and the code should be updated. If ordering matters we need to use a map
> that guarantees a given order, and hash map is not one of them.
>
> --Bobby Evans
>
> On 3/22/12 7:24 AM, "Kumar Ravi" <gokumarr...@gmail.com> wrote:
>
> Hello,
>
> We have been looking at IBM JDK junit failures on Hadoop-1.0.1
> independently and have ran into the same failures as reported in this
JIRA.
> I have a question based upon what I have observed below.
>
> We started debugging the problems in the testcase -
> org.apache.hadoop.mapred.lib.TestCombineFileInputFormat
> The testcase fails because the number of splits returned back from
> CombineFileInputFormat.getSplits() is 1 when using IBM JDK whereas the
> expected return value is 2.
>
> So far, we have found the reason for this difference in number of splits
is
> because the order in which elements in the rackToBlocks hashmap get
created
> is in the reverse order that Sun JDK creates.
>
> The question I have at this point is -- Should there be a strict
dependency
> in the order in which the rackToBlocks hashmap gets populated, to
determine
> the number of splits that get should get created in a hadoop cluster? Is
> this Working as designed?
>
> Regards,
> Kumar
>
>
>
