Mori Bellamy wrote:
i discovered that some of my code was causing out of bounds
exceptions. i cleaned up that code and the map tasks seemed to work.
that confuses me -- i'm pretty sure hadoop is resilient to a few map
tasks failing (5 out of 13k). before this fix, my remaining 2% of
tasks were getting killed.
Mori, I am not sure what the confusion is. Hadoop is resilient to few
task failures but not by default. The parameter that does it is
mapred.max.map.failures.percent and mapred.max.reduce.failures.percent.
Every task internally consists of attempts (internally, for the
framework). Hadoop allows some attempt failures too. If the number of
attempts that failed of a task exceeds the threshold
(mapred.map.max.attempts/mapred.reduce.max.attempts : default is 4) then
the task is considered failed. If the number of map/reduce task failures
exceeds the threshold
(mapred.max.map.failures.percent/mapred.max.reduce.failures.percent :
default is 0) then the job is considered failed.
Amar
On Jul 1, 2008, at 10:06 PM, Amar Kamat wrote:
Mori Bellamy wrote:
hey all,
i've got a mapreduce task that works on small (~1G) input. when i
try to run the same task on large (~100G) input, i get the following
error around when the map tasks are almost done (~98%)
2008-07-01 13:10:59,231 INFO org.apache.hadoop.mapred.ReduceTask:
task_200807011005_0005_r_000000_0: Got 0 new map-outputs & 0
obsolete map-outputs from tasktracker and 0 map-outputs from
previous failures
2008-07-01 13:10:59,232 INFO org.apache.hadoop.mapred.ReduceTask:
task_200807011005_0005_r_000000_0 Got 0 known map output
location(s); scheduling...
2008-07-01 13:10:59,232 INFO org.apache.hadoop.mapred.ReduceTask:
task_200807011005_0005_r_000000_0 Scheduled 0 of 0 known outputs (0
slow hosts and 0 dup hosts)
2008-07-01 13:10:59,232 INFO org.apache.hadoop.mapred.ReduceTask:
task_200807011005_0005_r_000000_0 Need 1 map output(s)
...
...
These are not error messages. The reducers are stuck as not all maps
are completed. Mori, could you let us know what is happening to the
other 2% maps. Are they getting executed? Are they still pending
(waiting to run)? Were they killed/failed? Is there any lost tracker?
I'm running the task on a cluster of 5 workers, one DFS master, and
one task tracker.
What do you mean by 5 workers and 1 task tracker?
i'm chaining mapreduce tasks, so i'm using SequenceFileOutput and
SequenceFileInput. this error happens before the first link in the
chain sucessfully reduces.
Can you elaborate this a bit. Are you chaining MR jobs?
Amar
does anyone have any insight? thanks!
