I have enough memory, so there will be only one sort and spill. Why do they will happen parallel?
2013/5/9 Robert Evans <[email protected]> > Yes it all happens in parallel even on a single task > > On 5/8/13 11:17 AM, "牛兆捷" <[email protected]> wrote: > > >I forget to say, for see the behavior of single task， I just run one map > >task for 1G input-split（I set block size to 1GB) > > > > > >2013/5/9 Robert Evans <[email protected]> > > > >> Deciding on the input split happens in the client. Each map process > >>just > >> opens up the input file and seeks to the appropriate offset in the file. > >> At that point it reads each entry one at a time and sends it to the map > >> task. The output of the map task is placed in a buffer. When the > >>buffer > >> gets close to full the data is sorted and spilled out to disk in > >>parallel > >> with the map task still running. It is hard to get CPU time for the > >> different parts because they are all happening in parallel. If you do > >>have > >> enough ram to store the entire output in memory and you have configured > >> your sort buffer to be able to hold it all then you will probably only > >> sort/spill once. > >> > >> --Bobby > >> > >> On 5/8/13 10:25 AM, "牛兆捷" <[email protected]> wrote: > >> > >> >I saw the application container log to trace the map-reduce > >>application. > >> > > >> >For map task, I find there are mainly 3 phase: spilit input, sort and > >> >spill > >> >out. > >> >I set the enough memory to make sure the input can stay in memory. > >> > > >> >Initially, I thought the highest cpu utilization will appear in sort > >>phase > >> >because the other two phase focus on IO,however, it doesn't behave as > >>what > >> >I thought. On the contrary, the cpu utilization during the other phase > >> >are > >> >higher. > >> > > >> >Anyone know the reason? > >> > > >> >-- > >> >*Sincerely,* > >> >*Zhaojie* > >> >* > >> >* > >> > >> > > > > > >-- > >*Sincerely,* > >*Zhaojie* > >* > >* > > -- *Sincerely,* *Zhaojie* * *
