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From Josh Wills <jwi...@cloudera.com>
Subject Re: Non Deterministic Record Drops
Date Tue, 28 Jul 2015 00:47:55 GMT
Hey Jeff,

Are the counts determined by Counters? Or is it the length of the output
files? Or both?

J

On Mon, Jul 27, 2015 at 5:29 PM, David Ortiz <dpo5003@gmail.com> wrote:

> Out of curiosity, any reason you went with multiple reads as opposed to
> just performing multiple operations on the same PTable? parallelDo returns
> a new object rather than modifying the initial one, so a single collection
> can start multiple execution flows.
>
> On Mon, Jul 27, 2015, 8:11 PM Jeff Quinn <jeff@nuna.com> wrote:
>
>> Hello,
>>
>> We have observed and replicated strange behavior with our crunch
>> application while running on MapReduce via the AWS ElasticMapReduce
>> service. Running a very simple job which is mostly map only, we see that an
>> undetermined subset of records are getting dropped. Specifically, we
>> expect 30,136,686 output records and have seen output on different trials
>> (running over the same data with the same binary):
>>
>> 22,177,119 records
>> 26,435,670 records
>> 22,362,986 records
>> 29,798,528 records
>>
>> These are all the things about our application which might be unusual and
>> relevant:
>>
>> - We use a custom file input format, via From.formattedFile. It looks
>> like this (basically a carbon copy
>> of org.apache.hadoop.mapreduce.lib.input.TextInputFormat):
>>
>> import org.apache.hadoop.io.LongWritable;
>> import org.apache.hadoop.io.Text;
>> import org.apache.hadoop.mapreduce.InputSplit;
>> import org.apache.hadoop.mapreduce.RecordReader;
>> import org.apache.hadoop.mapreduce.TaskAttemptContext;
>> import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
>> import org.apache.hadoop.mapreduce.lib.input.LineRecordReader;
>>
>> import java.io.IOException;
>>
>> public class ByteOffsetInputFormat extends FileInputFormat<LongWritable, Text>
{
>>
>>   @Override
>>   public RecordReader<LongWritable, Text> createRecordReader(
>>       InputSplit split, TaskAttemptContext context) throws IOException,
>>       InterruptedException {
>>     return new LineRecordReader();
>>   }
>> }
>>
>> - We call org.apache.crunch.Pipeline#read using this InputFormat many times, for
the job in question it is called ~160 times as the input is ~100 different files. Each file
ranges in size from 100MB-8GB. Our job only uses this input format for all input files.
>>
>> - For some files org.apache.crunch.Pipeline#read is called twice one the same file,
and the resulting PTables are processed in different ways.
>>
>> - It is only the data from these files which org.apache.crunch.Pipeline#read has
been called on more than once during a job that have dropped records, all other files consistently
do not have dropped records
>>
>> Curious if any Crunch users have experienced similar behavior before, or if any of
these details about my job raise any red flags.
>>
>> Thanks!
>>
>> Jeff Quinn
>>
>> Data Engineer
>>
>> Nuna
>>
>>
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>
>


-- 
Director of Data Science
Cloudera <http://www.cloudera.com>
Twitter: @josh_wills <http://twitter.com/josh_wills>

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