Hi,
Task attempt is an attempt to a task. At any given time, one or
more(speculative exec.) of task attempts can be running. For a task,
there can be many attempts at different nodes. A task is complete if any
of its attempts is complete. For a task to be marked as failed all of
mapred.map.max.attempts should fail. For every task in the job, a TaskID
is assigned. For every attempt, a TaskAttemptID is assigned (which ends
with _0, _1, etc).
Harish Mallipeddi wrote:
Hi,
Anyone can tell me what's the difference between "Killed Task Attempts" and
"Killed Tasks"? I ran a big job (14820 maps and 0 reduces). In the
job-details page, the web GUI reports 62 "killed task attempts". I'm
assuming this is due to "speculative execution". Now when I go to the
job-history page for the job, it reports 54 "killed tasks" (and 14820
successful map-tasks as expected).
A few questions:
* Why 62 killed task attempts vs 54 killed tasks?
* Under speculative execution, does hadoop launch a new MapTask with new
task-id or does it just launch a new MapTaskAttempt with a new
task-attempt-id?
* When a MapTaskAttempt fails, and when hadoop tries to re-launch the
MapTask, does it create a new task-id or just a new task-attempt-id?
* Does 'mapred.map.max.attempts' include all attempts launched due to
speculative-execution?
Btw this job is basically a trivial no-op job - it just scans around 1TB of
data and does nothing else in the map. I looked at the killed tasks' syslog
output and I didn't see any errors.
