Christian, The TaskTrackers send "heartbeat" messages to the JobTracker. The default interval for these messages is 3 seconds. This is one reason why you see the 3 second steps.
Abhishek On Mon, Apr 11, 2011 at 3:19 AM, Christian Kumpe <christ...@kumpe.de> wrote: > Hi, > > I'm doing some measurement on hadoop's execution time for my theses. I > discovered some steps in the jobs execution time when raising the > mappers' execution time continuously. > Here is a plot of the execution times with 1, 30 and 60 parallel > executing mappers: > http://baumbart.drhuim.de/executiontime.gif > > The cluster consists of 10 nodes and an overall map task capacity of 60. > I'm using hadoop 0.20.2. > > The many small steps about 1 second are probably caused by the polling > interval of the JobClient in monitorAndPrintJob(..) which is about 1 > second. > > But can anyone give me a hint, what's causing the bigger 3 second steps? > I suppose it's a polling interval, too. But where? In the Jobtracker? In > the Tasktrackers? > > Thanks for some help and comments, > Christian > >
