Hi Piyush,
I think you need to override the inbuilt partitioning function.
You can use function like (first field of key)%3
This will send all the keys with same first field to a separate reduce process
Please correct me if I am wrong.
Thanks
Utkarsh
From: Piyush Kansal [mailto:piyush.kan...@gmail.com]
Sent: Monday, February 20, 2012 7:39 AM
To: mapreduce-user@hadoop.apache.org
Subject: Query regarding Hadoop Partitioning
Hi Friends,
I have to sort huge amount of data in minimum possible time probably using
partitioning. The key is composed of 3 fields(partition, text and number). This
is how partition is defined:
* Partition "1" for range 1-10
* Partition "2" for range 11-20
* Partition "3" for range 21-30
I/P file format: partition[tab]text[tab]range-start[tab]range-end
[cloudera@localhost kMer2]$ cat input1
* 1 chr1 1 10
* 1 chr1 2 8
* 2 chr1 11 18
[cloudera@localhost kMer2]$ cat input2
* 1 chr1 3 7
* 2 chr1 12 19
[cloudera@localhost kMer2]$ cat input3
* 3 chr1 22 30
[cloudera@localhost kMer2]$ cat input4
* 3 chr1 22 30
* 1 chr1 9 10
* 2 chr1 15 16
Then I ran following command:
hadoop jar /usr/lib/hadoop/contrib/streaming/hadoop-streaming-0.20.2-cdh3u2.jar
\
-D stream.map.output.field.separator='\t' \
-D stream.num.map.output.key.fields=3 \
-D map.output.key.field.separator='\t' \
-D mapred.text.key.partitioner.options=-k1 \
-D mapred.reduce.tasks=3 \
-input /usr/pkansal/kMer2/ip \
-output /usr/pkansal/kMer2/op \
-mapper /home/cloudera/kMer2/kMer2Map.py \
-file /home/cloudera/kMer2/kMer2Map.py \
-reducer /home/cloudera/kMer2/kMer2Red.py \
-file /home/cloudera/kMer2/kMer2Red.py
Both mapper and reducer scripts just contain one line of code:
for line in sys.stdin:
line = line.strip()
print "%s" % (line)
Following is the o/p:
[cloudera@localhost kMer2]$ hadoop dfs -cat /usr/pkansal/kMer2/op/part-00000
* 2 chr1 12 19
* 2 chr1 15 16
* 3 chr1 22 30
* 3 chr1 22 30
[cloudera@localhost kMer2]$ hadoop dfs -cat /usr/pkansal/kMer2/op/part-00001
* 1 chr1 2 8
* 1 chr1 3 7
* 1 chr1 9 10
* 2 chr1 11 18
[cloudera@localhost kMer2]$ hadoop dfs -cat /usr/pkansal/kMer2/op/part-00002
* 1 chr1 1 10
* 3 chr1 22 29
This is not the o/p which I expected. I expected all records with:
* partition 1 in one single file eg part-m-00000
* partition 2 in one single file eg part-m-00001
* partition 3 in one single file eg part-m-00002
Can you please suggest if I am doing it in a right way?
--
Regards,
Piyush Kansal
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