[MAPREDUCE-3226] Few reduce tasks hanging in a gridmix-run

• Type: Bug
• Status: Closed
• Priority: Blocker
• Resolution: Fixed
• Affects Version/s: 0.23.0
• Fix Version/s: 0.23.0
• Component/s: mrv2, task
• Assignee: Vinod Kumar Vavilapalli
• Reporter: Vinod Kumar Vavilapalli
• Created: 20/Oct/11 06:38
• Updated: 15/Nov/11 00:49
• Resolved: 20/Oct/11 22:45

Description

In a gridmix run with ~1000 jobs, one job is getting stuck because of 2-3 hanging reducers. All of the them are stuck after downloading all map outputs and have the following thread dump.

"EventFetcher for fetching Map Completion Events" daemon prio=10 tid=0xa325fc00 nid=0x1ca4 waiting on condition [0xa315c000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
        at java.lang.Thread.sleep(Native Method)
        at org.apache.hadoop.mapreduce.task.reduce.EventFetcher.run(EventFetcher.java:71)

"main" prio=10 tid=0x080ed400 nid=0x1c71 in Object.wait() [0xf73a2000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0xa94b23d8> (a org.apache.hadoop.mapreduce.task.reduce.EventFetcher)
        at java.lang.Thread.join(Thread.java:1143)
        - locked <0xa94b23d8> (a org.apache.hadoop.mapreduce.task.reduce.EventFetcher)
        at java.lang.Thread.join(Thread.java:1196)
        at org.apache.hadoop.mapreduce.task.reduce.Shuffle.run(Shuffle.java:135)
        at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:367)
        at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:147)
        at java.security.AccessController.doPrivileged(Native Method)
        at javax.security.auth.Subject.doAs(Subject.java:396)
        at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1135)
        at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:142)

Thanks to karams for helping track this down.