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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-6072) distcp should place the file distcp_src_files in distributed cache
Date Fri, 19 Jun 2009 17:42:07 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-6072?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Doug Cutting updated HADOOP-6072:
---------------------------------

    Comment: was deleted

(was: Some comments:
 - 'sleeptime' should be 'getSleeptime()' to be thread safe, no?  or maybe use int as a sleep
time, since updates to an int are atomic.
 - getNumRunningMaps() is expensive to call from each node at each interval, since reports
for all tasks must be retrieved from the JT.  better would be to just fetch the job's counters
each time, since they're constant-sized, not proportional to the number of tasks.  You'd need
to add a maps_completed counter, then use the difference between that and TOTAL_LAUNCHED_MAPS
to calculate the number running.
 - the interval to contact the JT might be randomized a bit, so that not all tasks hit it
at the same time, e.g., by adding a random value that's 10% of the specified value.
 - when InterruptedException is caught a thread should generally exit, not simply log a warning.
 if things will no longer work correctly without the thread, then it should somehow cause
other threads dependent threads to fail too.
 - getNumRunningMaps() should either return a correct value or throw an exception.  if it
cannot contact the JT or if the task does not know its Id it should fail, no?)

> distcp should place the file distcp_src_files in distributed cache
> ------------------------------------------------------------------
>
>                 Key: HADOOP-6072
>                 URL: https://issues.apache.org/jira/browse/HADOOP-6072
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: tools/distcp
>    Affects Versions: 0.21.0
>            Reporter: Ravi Gummadi
>            Assignee: Ravi Gummadi
>             Fix For: 0.21.0
>
>         Attachments: d_replica_srcfilelist.patch
>
>
> When large number of files are being copied by distcp, accessing distcp_src_files seems
to be an issue, as all map tasks would be accessing this file. The error message seen is:
> 09/06/16 10:13:16 INFO mapred.JobClient: Task Id : attempt_200906040559_0110_m_003348_0,
Status : FAILED
> java.io.IOException: Could not obtain block: blk_-4229860619941366534_1500174
> file=/mapredsystem/hadoop/mapredsystem/distcp_7fiyvq/_distcp_src_files
>         at org.apache.hadoop.hdfs.DFSClient$DFSInputStream.chooseDataNode(DFSClient.java:1757)
>         at org.apache.hadoop.hdfs.DFSClient$DFSInputStream.blockSeekTo(DFSClient.java:1585)
>         at org.apache.hadoop.hdfs.DFSClient$DFSInputStream.read(DFSClient.java:1712)
>         at java.io.DataInputStream.readFully(DataInputStream.java:178)
>         at java.io.DataInputStream.readFully(DataInputStream.java:152)
>         at org.apache.hadoop.io.SequenceFile$Reader.init(SequenceFile.java:1450)
>         at org.apache.hadoop.io.SequenceFile$Reader.<init>(SequenceFile.java:1428)
>         at org.apache.hadoop.io.SequenceFile$Reader.<init>(SequenceFile.java:1417)
>         at org.apache.hadoop.io.SequenceFile$Reader.<init>(SequenceFile.java:1412)
>         at org.apache.hadoop.mapred.SequenceFileRecordReader.<init>(SequenceFileRecordReader.java:43)
>         at org.apache.hadoop.tools.DistCp$CopyInputFormat.getRecordReader(DistCp.java:299)
>         at org.apache.hadoop.mapred.MapTask.runOldMapper(MapTask.java:336)
>         at org.apache.hadoop.mapred.MapTask.run(MapTask.java:305)
>         at org.apache.hadoop.mapred.Child.main(Child.java:170)
> This could be because of HADOOP-6038 and/or HADOOP-4681.
> If distcp places this special file distcp_src_files in distributed cache, that could
solve the problem.

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