RE: Map tasks processing some files multiple times

[David Parks]

I believe I just tracked down the problem, maybe you can help confirm if you’re 
familiar with this.

 

I see that FileInputFormat is specifying that gzip files (.gz extension) from 
s3n filesystem are being reported as splittable, and I see that it’s creating 
multiple input splits for these files. I’m mapping the files directly off S3:

 

       Path lsDir = new 
Path("s3n://fruggmapreduce/input/catalogs/linkshare_catalogs/*~*");

       MultipleInputs.addInputPath(job, lsDir, FileNameTextInputFormat.class, 
LinkShareCatalogImportMapper.class);

 

I see in the map phase, based on my counters, that it’s actually processing the 
entire file (I set up a counter per file input). So the 2 files which were 
processed twice had 2 splits (I now see that in some debug logs I created), and 
the 1 file that was processed 3 times had 3 splits (the rest were smaller and 
were only assigned one split by default anyway).

 

Am I wrong in expecting all files on the s3n filesystem to come through as 
not-splittable? This seems to be a bug in hadoop code if I’m right.

 

David

 

 

From: Raj Vishwanathan [mailto:rajv...@yahoo.com] 
Sent: Thursday, December 06, 2012 1:45 PM
To: user@hadoop.apache.org
Subject: Re: Map tasks processing some files multiple times

 

Could it be due to spec-ex? Does it make a diffrerence in the end?

 

Raj

 


  _____  


From: David Parks <davidpark...@yahoo.com>
To: user@hadoop.apache.org 
Sent: Wednesday, December 5, 2012 10:15 PM
Subject: Map tasks processing some files multiple times

 

I’ve got a job that reads in 167 files from S3, but 2 of the files are being 
mapped twice and 1 of the files is mapped 3 times.

 

This is the code I use to set up the mapper:

 

       Path lsDir = new 
Path("s3n://fruggmapreduce/input/catalogs/linkshare_catalogs/*~*");

       for(FileStatus f : lsDir.getFileSystem(getConf()).globStatus(lsDir)) 
log.info("Identified linkshare catalog: " + f.getPath().toString());

       if( lsDir.getFileSystem(getConf()).globStatus(lsDir).length > 0 ){

              MultipleInputs.addInputPath(job, lsDir, 
FileNameTextInputFormat.class, LinkShareCatalogImportMapper.class);

       }

 

I can see from the logs that it sees only 1 copy of each of these files, and 
correctly identifies 167 files.

 

I also have the following confirmation that it found the 167 files correctly:

 

2012-12-06 04:56:41,213 INFO 
org.apache.hadoop.mapreduce.lib.input.FileInputFormat (main): Total input paths 
to process : 167

 

When I look through the syslogs I can see that the file in question was opened 
by two different map attempts:

 

./task-attempts/job_201212060351_0001/attempt_201212060351_0001_m_000005_0/syslog:2012-12-06
 03:56:05,265 INFO org.apache.hadoop.fs.s3native.NativeS3FileSystem (main): 
Opening 
's3n://fruggmapreduce/input/catalogs/linkshare_catalogs/linkshare~CD%20Universe~85.csv.gz'
 for reading

./task-attempts/job_201212060351_0001/attempt_201212060351_0001_m_000173_0/syslog:2012-12-06
 03:53:18,765 INFO org.apache.hadoop.fs.s3native.NativeS3FileSystem (main): 
Opening 
's3n://fruggmapreduce/input/catalogs/linkshare_catalogs/linkshare~CD%20Universe~85.csv.gz'
 for reading

 

This is only happening to these 3 files, all others seem to be fine. For the 
life of me I can’t see a reason why these files might be processed multiple 
times.

 

Notably, map attempt 173 is more map attempts than should be possible. There 
are 167 input files (from S3, gzipped), thus there should be 167 map attempts. 
But I see a total of 176 map tasks.

 

Any thoughts/ideas/guesses?