Thanks Nick, but "in-memory" means a combiner can only be used over a single mapper?right?! Is there a way we use it for several mappers as well? Also what do you mean by "it may or may not run on a particular map attempt"?
Br, Jackob On Mon, Aug 2, 2010 at 5:43 PM, Nick Jones <[email protected]> wrote: > Hi Jackob, > A combiner acts a lot like a reduce step but it's executed on the mapper > with in-memory data. I've seen a reduction in job execution time by adding > one. The one caveat to keep in mind is that it may or may not run on a > particular map attempt. > > Nick > > > > On 8/2/2010 10:39 AM, Jackob Carlsson wrote: > >> Hi everyone, >> Could anyone please help me to understand the function of combiner? >> >> Thanks in advance >> Jackob >> >> > >
