[MAPREDUCE-646] distcp should place the file distcp_src_files in distributed cache

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.21.0
• Component/s: distcp
• Hadoop Flags: Reviewed
• Release Note: Patch increases the replication factor of _distcp_src_files to sqrt(min(maxMapsOnCluster, totalMapsInThisJob)) sothat many maps won't access the same replica of the file _distcp_src_files at the same time.
• Assignee: Ravi Gummadi
• Reporter: Ravi Gummadi
• Created: 17/Jun/09 19:52
• Updated: 24/Aug/10 21:14
• Resolved: 29/Jun/09 18:21

Description

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.