i believe so, yes: but note that individual reducer task needs to finish, not just when processing a given key/value pair
Miles 2008/11/3 Ryan LeCompte <[EMAIL PROTECTED]>: > What happens when the reducer task gets invoked more than once? My > guess is once a reducer task finishes writing the data for a > particular key to HDFS, it won't somehow get re-executed again for the > same key right? > > > On Mon, Nov 3, 2008 at 11:28 AM, Miles Osborne <[EMAIL PROTECTED]> wrote: >> you can't guarantee that a reducer (or mapper for that matter) will be >> executed exactly once unless you turn-off preemptive scheduling. but, >> a distinct key gets sent to a single reducer, so yes, only one reducer >> will see a particulat key + associated values >> >> Miles >> >> 2008/11/3 Ryan LeCompte <[EMAIL PROTECTED]>: >>> Hello, >>> >>> Is it safe to assume that only one reduce task will ever operate on >>> values for a particular key? Or is it possible that more than one >>> reduce task can work on values for the same key? The reason I ask is >>> because I want to ensure that a piece of code that I write at the end >>> of my reducer method will only ever be executed once after all values >>> for a particular key are aggregated/summed. >>> >>> Thanks, >>> Ryan >>> >> >> >> >> -- >> The University of Edinburgh is a charitable body, registered in >> Scotland, with registration number SC005336. >> > -- The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336.
