You would only be able to set it for the script... which means it will apply to all 8 jobs. However, my guess is that you don't need to control the number of map tasks per machine.
On Sun, Nov 3, 2013 at 4:21 PM, John <johnnyenglish...@gmail.com> wrote: > Thanks for your answer! How can I set the mapred.tasktracker.map.tasks. > maxiumum value only for this speficic job? For example the pig script is > creating 8 jobs, and I only want to modify this value for the first job? I > think there is no option in PigLatin to influence this value? > > kind regards > > > > > 2013/11/4 Pradeep Gollakota <pradeep...@gmail.com> > > > I think you’re misunderstanding how HBaseStorage works. HBaseStorage uses > > the HBaseInputFormat underneath the hood. The number of map tasks that > are > > spawned is dependent on the number of regions you have. The map tasks are > > spawned such that the tasks are local to the regions they’re reading > from. > > You will typically not have to worry about problems such as this with > > MapReduce. If you do have some performance concerns, you can set the > > mapred.tasktracker.map.tasks.maxiumum setting in the job conf and it will > > not affect all the other jobs. > > > > > > On Sun, Nov 3, 2013 at 3:04 PM, John <johnnyenglish...@gmail.com> wrote: > > > > > Hi, > > > > > > is it possible to limit the number of map slots used for the load > > function? > > > For example I have 5 nodes with 10 map slots (each node has 2 slots for > > > every cpu) I want only one map task for every node. Is there a way to > set > > > this only for the load function? I know there is a option called > > > "mapred.tasktracker.map.tasks.maximum", > > > but this would influence every MapReduce job. I want to influence the > > > number only for this specific job. > > > > > > My use case is the following: I'm using a modified version of the > > > HBaseStorage function. I try to load for example 10 different rowkeys > > with > > > very big column sizes and join them afterwords. Since the columns all > > have > > > the same column family every row can be stored to a different server. > For > > > example rowkey rowkey 1-5 is stored on node1 and the other rowkeys on > the > > > other nodes. So If I create a Pig script to load the 10 keys and join > > them > > > afterwards this will end up in 1 MapReduce Job with 10 map task and > some > > > reduce tasks (depends on the parallel factor). The problem is that > there > > > will be created 2 map tasks on node1, because there are 2 slots > > available. > > > This means every task is reading simultaneously a large number of > columns > > > from the local hard drive. Maybe I'm wrong, but this should be a > > > performance issue?! It should be faster if to read each rowkey one > after > > > another!? > > > > > > kind regards > > > > > >
