[Hadoop-common-user] Chaining Multiple Map reduce jobs.

On Wed, Apr 8, 2009 at 11:30 PM, asif md wrote:

hi everyone,

i have to chain multiple map reduce jobs < actually 2 to 4 jobs >, each of
the jobs depends on the o/p of preceding job. In the reducer of each job
I'm
doing very little < just grouping by key from the maps>. I want to give the
output of one MapReduce job to the next job without having to go to the
disk. Does anyone have any ideas on how to do this?

Thanx.

On Apr 8, 2009, at 3:14 PM, Lukáš Vlček wrote:

Hi,
by far I am not an Hadoop expert but I think you can not start Map
task
until the previous Reduce is finished. Saying this it means that you
probably have to store the Map output to the disk first (because a]
it may
not fit into memory and b] you would risk data loss if the system
crashes).
As for the job chaining you can check JobControl class (
http://hadoop.apache.org/core/docs/current/api/org/apache/hadoop/mapred/jobcontrol/JobControl.html)
<http://hadoop.apache.org/core/docs/current/api/org/apache/hadoop/mapred/jobcontrol/JobControl.html
Also you can look at https://issues.apache.org/jira/browse/HADOOP-3702

Regards,
Lukas


--
http://blog.lukas-vlcek.com/

On Wed, Apr 8, 2009 at 3:30 PM, Nathan Marz wrote:

You can also try decreasing the replication factor for the intermediate
files between jobs. This will make writing those files faster.


On Apr 8, 2009, at 3:14 PM, Lukáš Vlček wrote:

Hi,