Setting slowstart to 1 would only control when reduces get started wrt that particular job's maps (doesn't prevent the reduce task from some other job to be scheduled alongside the map task from this job on a TT). So this doesn't meet the OP's requirement - a TT should only run 1 map or 1 reduce task at a time. There's no easy way to achieve this I'm afraid.
On Sat, Sep 26, 2009 at 3:02 AM, Chandraprakash Bhagtani < [email protected]> wrote: > you can control that by property > > <property> > > <name>mapred.reduce.slowstart.completed.maps</name> > > <value>0.05</value> > > <description>Fraction of the number of maps in the job which should be > > complete before reduces are scheduled for the job. > > </description> > > </property> > set the value of this property to 1. It will start the reducers when all > the > maps will finish. > This will work with hadoop version 0.20.0. > On Fri, Sep 25, 2009 at 8:39 PM, Steve Loughran <[email protected]> wrote: > > > Oliver Senn wrote: > > > >> Hi, > >> > >> Thanks for your answer. > >> > >> I used these parameters. But they seem to limit only the number of > >> parallel maps and parallel reduces separately. They do not prevent the > >> scheduler from schedule one map and one reduce on the same task tracker > in > >> parallel. > >> > >> But that's the problem I'm trying to solve. Having at most one task > >> running on a task tracker at any time (never one map and one reduce > together > >> on one task tracker). > >> > >> > > You could do your own scheduler, if you really can't handle the things in > > parallel > > > > > > -- > Thanks & Regards, > Chandra Prakash Bhagtani, > -- Harish Mallipeddi http://blog.poundbang.in
