Well, the only way to reliably fix the number of maptasks that I've found is by using compressed input files, that forces hadoop to assign one and only one file to a map task ;)
Andreas On Thursday 31 July 2008 21:30:33 Gopal Gandhi wrote: > Thank you, finally someone has interests in my questions =) > My cluster contains more than one machine. Please don't get me wrong :-). I > don't want to limit the total mappers in one node (by mapred.map.tasks). > What I want is to limit the total mappers for one job. The motivation is > that I have 2 jobs to run at the same time. they have "the same input data > in Hadoop". I found that one job has to wait until the other finishes its > mapping. Because the 2 jobs are submitted by 2 different people, I don't > want one job to be starving. So I want to limit the first job's total > mappers so that the 2 jobs will be launched simultaneously. > > > > ----- Original Message ---- > From: "Goel, Ankur" <[EMAIL PROTECTED]> > To: core-user@hadoop.apache.org > Cc: [EMAIL PROTECTED] > Sent: Wednesday, July 30, 2008 10:17:53 PM > Subject: RE: How can I control Number of Mappers of a job? > > How big is your cluster? Assuming you are running a single node cluster, > > Hadoop-default.xml has a parameter 'mapred.map.tasks' that is set to 2. > So > By default, no matter how many map tasks are calculated by framework, > only 2 map task will execute on a single node cluster. > > -----Original Message----- > From: Gopal Gandhi [mailto:[EMAIL PROTECTED] > Sent: Thursday, July 31, 2008 4:38 AM > To: core-user@hadoop.apache.org > Cc: [EMAIL PROTECTED] > Subject: How can I control Number of Mappers of a job? > > The motivation is to control the max # of mappers of a job. For example, > the input data is 246MB, divided by 64M is 4. If by default there will > be 4 mappers launched on the 4 blocks. > What I want is to set its max # of mappers as 2, so that 2 mappers are > launched first and when they completes on the first 2 blocks, another 2 > mappers start on the rest 2 blocks. Does Hadoop provide a way?
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