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.
