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From Björn-Elmar Macek <ma...@cs.uni-kassel.de>
Subject Re: OutputValueGroupingComparator gets strange inputs (topic changed from "Logs cannot be created")
Date Thu, 09 Aug 2012 15:14:05 GMT
Ah ok, i got the idea: i can use the abstract class instead of the low 
level interface, though i am not sure, how to use it. It would just be 
nice, if complexer mechanics like the sorting would have an up-to-date 
tutorial with some example code. If i find the time, i will make one, 
since i want to make a presentation for Hadoop anyways.

Thanks for your help! I will try to use the abstract class.


Am 09.08.2012 17:03, schrieb Björn-Elmar Macek:
> Hi Bertrand,
>
> i am using RawComperator because this one was used in the tutorial of 
> some famous (hadoop) guy describing how to sort the input for the 
> reducer. Is there an easier alternative?
>
>
> Am 09.08.2012 16:57, schrieb Bertrand Dechoux:
>> I am just curious but are you using Writable? If so there is a 
>> WritableComparator...
>> If you are going to interpret every bytes (you create a String, so 
>> you do), there no clear reason for choosing such a low level API.
>>
>> Regards
>>
>> Bertrand
>>
>> On Thu, Aug 9, 2012 at 4:47 PM, Björn-Elmar Macek 
>> <macek@cs.uni-kassel.de <mailto:macek@cs.uni-kassel.de>> wrote:
>>
>>     Hi again,
>>
>>     this is an direct response to my previous posting with the title
>>     "Logs cannot be created", where logs could not be created (Spill
>>     failed). I got the hint, that i gotta check privileges, but that
>>     was not the problem, because i own the folders that were used for
>>     this.
>>
>>     I finally found an important hint in a log saying:
>>     12/08/09 15:30:49 WARN mapred.JobClient: Error reading task
>>     outputhttp://its-cs229.its.uni-kassel.de:50060/tasklog?plaintext=true&attemptid=attempt_201208091516_0001_m_000048_0&filter=stdout
>>     <http://its-cs229.its.uni-kassel.de:50060/tasklog?plaintext=true&attemptid=attempt_201208091516_0001_m_000048_0&filter=stdout>
>>     12/08/09 15:30:49 WARN mapred.JobClient: Error reading task
>>     outputhttp://its-cs229.its.uni-kassel.de:50060/tasklog?plaintext=true&attemptid=attempt_201208091516_0001_m_000048_0&filter=stderr
>>     <http://its-cs229.its.uni-kassel.de:50060/tasklog?plaintext=true&attemptid=attempt_201208091516_0001_m_000048_0&filter=stderr>
>>     12/08/09 15:34:34 INFO mapred.JobClient: Task Id :
>>     attempt_201208091516_0001_m_000055_0, Status : FAILED
>>     java.io.IOException: Spill failed
>>             at
>>     org.apache.hadoop.mapred.MapTask$MapOutputBuffer.collect(MapTask.java:1029)
>>             at
>>     org.apache.hadoop.mapred.MapTask$OldOutputCollector.collect(MapTask.java:592)
>>             at
>>     uni.kassel.macek.rtprep.RetweetMapper.map(RetweetMapper.java:26)
>>             at
>>     uni.kassel.macek.rtprep.RetweetMapper.map(RetweetMapper.java:12)
>>             at org.apache.hadoop.mapred.MapRunner.run(MapRunner.java:50)
>>             at
>>     org.apache.hadoop.mapred.MapTask.runOldMapper(MapTask.java:436)
>>             at org.apache.hadoop.mapred.MapTask.run(MapTask.java:372)
>>             at org.apache.hadoop.mapred.Child$4.run(Child.java:255)
>>             at java.security.AccessController.doPrivileged(Native Method)
>>             at javax.security.auth.Subject.doAs(Subject.java:396)
>>             at
>>     org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1093)
>>             at org.apache.hadoop.mapred.Child.main(Child.java:249)
>>     Caused by: java.lang.NumberFormatException: For input string: ""
>>             at
>>     java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
>>             at java.lang.Integer.parseInt(Integer.java:468)
>>             at java.lang.Integer.parseInt(Integer.java:497)
>>             at uni.kassel.macek.rtprep.Tweet.getRT(Tweet.java:126)
>>             at
>>     uni.kassel.macek.rtprep.TwitterValueGroupingComparator.compare(TwitterValueGroupingComparator.java:47)
>>             at
>>     org.apache.hadoop.mapred.MapTask$MapOutputBuffer.compare(MapTask.java:1111)
>>             at
>>     org.apache.hadoop.util.QuickSort.sortInternal(QuickSort.java:95)
>>             at org.apache.hadoop.util.QuickSort.sort(QuickSort.java:59)
>>             at
>>     org.apache.hadoop.mapred.MapTask$MapOutputBuffer.sortAndSpill(MapTask.java:1399)
>>             at
>>     org.apache.hadoop.mapred.MapTask$MapOutputBuffer.access$1800(MapTask.java:853)
>>             at
>>     org.apache.hadoop.mapred.MapTask$MapOutputBuffer$SpillThread.run(MapTask.java:1344)
>>
>>
>>
>>     corresponding to the following lines of code within the class
>>     TwitterValueGroupingComparator:
>>
>>     public class TwitterValueGroupingComparator implements
>>     RawComparator<Text> {
>>     ...
>>         public int compare(byte[] text1, int start1, int length1,
>>     byte[] text2,
>>             int start2, int length2) {
>>
>>         byte[] tweet1 = new byte[length1];// length1-1 (???)
>>         byte[] tweet2 = new byte[length2];// length1-1 (???)
>>
>>         System.arraycopy(text1, start1, tweet1, 0, length1);//
>>     start1+1 (???)
>>         System.arraycopy(text2, start2, tweet2, 0, length2);//
>>     start2+1 (???)
>>
>>         Tweet atweet1 = new Tweet(new String(tweet1));
>>         Tweet atweet2 = new Tweet(new String(tweet2));
>>
>>
>>         String key1 = atweet1.getAuthor();
>>         String key2 = atweet2.getAuthor();
>>     ////////////////////////////////////////////////////////////////
>>     //THE FOLLOWING LINE IS THE ONE MENTIONED IN THE LOG (47)
>>     /////////////////////////////////////////////////////////////////
>>         if (atweet1.getRT() > 0 && !atweet1.getMention().equals(""))
>>             key1 = atweet1.getMention();
>>         if (atweet2.getRT() > 0 && !atweet2.getMention().equals(""))
>>             key2 = atweet2.getMention();
>>
>>         int realKeyCompare = key1.compareTo(key2);
>>         return realKeyCompare;
>>         }
>>
>>     }
>>
>>     As i am taking the incoming bytes and interpret them as Tweets by
>>     recreating the appropriate CSV-Strings and Tokenizing it, i was
>>     kind of sure, that the problem somehow are the leading bytes,
>>     that Hadoop puts in front of the data being compared. Since i
>>     never really understood what hadoop is doing to the strings when
>>     they are sent to the KeyComparator  i simply appended all strings
>>     to a file in order to see myself.
>>
>>     You can see the results here:
>>
>>     ??2009-06-12 07:32:47, davedilbeck, tampabaycom, , ,
>>     http://tinyurl.com/nookw7, 1, 1, Lots of vivid imagery here but
>>     it's mostly bullshit   Alex Sink June Cleaver or Joan Crawford, null
>>     ??2009-06-12 07:32:47, davedilbeck, tampabaycom, , ,
>>     http://tinyurl.com/nookw7, 1, 1, Lots of vivid imagery here but
>>     it's mostly bullshit   Alex Sink June Cleaver or Joan Crawford, null
>>     I2009-06-12 04:33:19, ntmp, tsukunep, , , , 1, 0,
>>     ??????????????????, null
>>     ??2009-06-12 07:32:47, davedilbeck, tampabaycom, , ,
>>     http://tinyurl.com/nookw7, 1, 1, Lots of vivid imagery here but
>>     it's mostly bullshit   Alex Sink June Cleaver or Joan Crawford, null
>>     ^2009-06-12 04:33:20, aclouatre, , , , , 0, 0, Bored out of my
>>     mind Watching food network, null
>>     b2009-06-12 04:33:20, djnewera, adoremii369, , , , 1, 0, LOL
>>     WORDUP ANT NOTHING LIKE THE HOOD, null
>>
>>
>>     As you can see there are different leading characters: sometimes
>>     its "??", other times its "b" or "^", etc.
>>
>>     My question is now:
>>     How many bits do i have to cut off, so i get the original Text as
>>     a String that i put into the key-position of my mapper output?
>>     What are the concepts behind this?
>>
>>     Thanks for your help in advance!
>>
>>     Best regards,
>>     Elmar Macek
>>
>>
>>
>>
>>
>>
>> -- 
>> Bertrand Dechoux
>
>



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