Engineering Blog


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Automatic logging of MapReduce task failures

When using Cascading to run MapReduce jobs in production, the most common exception we find in our job logs look like this: Caused by: cascading.flow.FlowException: step failed: (1/1), with job id: job_201307251526_37599, please see cluster logs for failure messages at cascading.flow.planner.FlowStepJob.blockOnJob( at cascading.flow.planner.FlowStepJob.start( at at at java.util.concurrent.FutureTask$Sync.innerRun( at at java.util.concurrent.ThreadPoolExecutor$Worker.runTask( at java.util.concurrent.ThreadPoolExecutor$ at This exception tells us that the job failed ...

Debugging “ClassCastException:” exceptions when testing Cascading flows

When testing our Hadoop data workflows we've intermittently run into this error, which ends up failing the MapReduce job being tested: java.lang.ClassCastException: cannot be cast to org.apache.hadoop.mapred.FileSplit at org.apache.hadoop.mapred.TextInputFormat.getRecordReader( at org.apache.hadoop.mapred.MapTask.runOldMapper( at A quick search for the error didn't find any obvious problems. When we dug into the problem a a bit more, we noticed a couple ...