Database Reference
In-Depth Information
As the map or reduce task runs, the child process communicates with its parent applica-
tion master through the
umbilical
interface. The task reports its progress and status (in-
cluding counters) back to its application master, which has an aggregate view of the job,
every three seconds over the umbilical interface.
The resource manager web UI displays all the running applications with links to the web
UIs of their respective application masters, each of which displays further details on the
MapReduce job, including its progress.
During the course of the job, the client receives the latest status by polling the application
master every second (the interval is set via
mapre-
duce.client.progressmonitor.pollinterval
). Clients can also use
Job
's
getStatus()
method to obtain a
JobStatus
instance, which contains all of the
status information for the job.
The process is illustrated in
Figure 7-3
.
