Great News !! Thanks for the info. So using reflection, I can inject different implementations of interfaces (services) for the mapper (or reducer). And this way I can test a mapper (or reducer). Just by reflecting a stub instead of a real implementation.
Thanks, Eyal Golan [email protected] Visit: http://jvdrums.sourceforge.net/ LinkedIn: http://www.linkedin.com/in/egolan74 Skype: egolan74 P Save a tree. Please don't print this e-mail unless it's really necessary On Fri, Dec 30, 2011 at 2:50 PM, Harsh J <[email protected]> wrote: > Eyal, > > Yes, it is right to think of each Task attempt being one individual JVM > running individually on any added Node. Multiple slots would mean multiple > VMs in parallel as well. Yes, your use of reflection to build your objects > will work just fine -- its all user-side java code that is executed. > > On 30-Dec-2011, at 4:42 PM, Eyal Golan wrote: > > Hi, > > I want to understand a basic concept in MR. > > If a mapper creates an instance of some class (using the 'new' operator), > then the created class exists ONCE in the VM of this node. > For each node. > Correct? > > Now, > what if instead of using the 'new' operator, the class is created using > reflection. > Is it valid in a MR? > Will only one instance of the created class be existing in that node? > > Thanks, > > > Eyal > > Eyal Golan > [email protected] > > Visit: http://jvdrums.sourceforge.net/ > LinkedIn: http://www.linkedin.com/in/egolan74 > Skype: egolan74 > > P Save a tree. Please don't print this e-mail unless it's really necessary > > >
