Ok, that is what I wanted to know. Thanks you!
Best Regards, Lucian On Fri, Jul 1, 2011 at 2:47 PM, Devaraj K <devara...@huawei.com> wrote: > Hi Lucian,**** > > ** ** > > For every map task, combiner will be executed multiple times > before writing the map output. Combine step is not a separate task and it is > part of map task execution. Reducer will copy the output of the map task > which is reduced by the combiner.**** > > ** ** > > >For example: > >If I have *2 map tasks* ran on the same machine, will I have *1 combine > task* on that machine to combine the maps outputs, *or 2 combine tasks*?** > ** > > ** ** > > In this case, combiner will be executed for each map task independent to > each other. This combiner step will execute multiple times till it gets same > output for 1 or more runs of combiner. > > **** > > ** ** > > You can go through Combiner section here for more info : > http://wiki.apache.org/hadoop/HadoopMapReduce**** > > ** ** > > Devaraj K **** > > > ------------------------------------------------------------------------------------------------------------------------------------- > This e-mail and its attachments contain confidential information from > HUAWEI, which > is intended only for the person or entity whose address is listed above. > Any use of the > information contained herein in any way (including, but not limited to, > total or partial > disclosure, reproduction, or dissemination) by persons other than the > intended > recipient(s) is prohibited. If you receive this e-mail in error, please > notify the sender by > phone or email immediately and delete it!ss**** > > **** > ------------------------------ > > *From:* Lucian Iordache [mailto:lucian.george.iorda...@gmail.com] > *Sent:* Friday, July 01, 2011 2:25 PM > *To:* mapreduce-user@hadoop.apache.org > *Subject:* Relation between Mapper and Combiner**** > > ** ** > > Hello guys, > > Can anybody tell me which is the relation between map task and combine > tasks? > I would like to know if there is a 1:1 relation between them, or is a *:1 > (many to one). > > For example: > If I have *2 map tasks* ran on the same machine, will I have *1 combine > task* on that machine to combine the maps outputs, *or 2 combine tasks*? > > Best Regards, > -- > Lucian**** >
