Archivo de la etiqueta: MapReduce

S3 and Parallel Processing – DirectFileOutputCommitter


The problem: While a Hadoop Job is writing output, it will write to a temporary directory: Task1 –> /unique/temp/directory/task1/file.tmp Task2 –> /unique/temp/directory/task2/file.tmp When the tasks finish the execution, will move (commit) the temporary file to a final location. This schema … Seguir leyendo

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Copy Data with Hive and Spark / Copiar Datos con Hive y Spark


These are two examples of how to copy data from one S3 location to other S3 location. Same operation can be done from S3 to HDFS and vice-versa. I’m considering that you are able to launch the Hive client or … Seguir leyendo

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HBase and Zookeeper debugging


I came across some scenarios where an application (i.e. Mapreduce) communicating to HBase through YARN could silently fail with a timeout like the following: 2017-01-30 19:42:03,657 DEBUG [main] org.apache.hadoop.hbase.client.ConnectionManager$HConnectionImplementation: locateRegionInMeta parentTable=hbase:meta, metaLocation=, attempt=9 of 35 failed; retrying after sleep of … Seguir leyendo

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FileInputFormat vs. CombineFileInputFormat


When you put a file into HDFS, it is converted to blocks of 128 MB. (Default value for HDFS on EMR) Consider a file big enough to consume 10 blocks. When you read that file from HDFS as an input … Seguir leyendo

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Hadoop: Output Commiter Notes


OutputCommitter describes the commit of task output for a MapReduce job. The MapReduce framework relies on the OutputCommitter of the job to: Set up the job during initialization; for example, create the temporary output directory for the job. Job setup … Seguir leyendo

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YARN / Map Reduce memory settings


On Hadoop 1, we used to use mapred.child.java.opts to set the Java Heap size for the task tracker child processes. With YARN, that parameter has been deprecated in favor of: mapreduce.map.java.opts – These parameter is passed to the JVM for mappers. … Seguir leyendo

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Hadoop 1 vs Hadoop 2


There are a lot of articles about this, but, I just needed a good summary of concepts: Hadoop 1: A master process called the JobTracker is the central scheduler for all MapReduce jobs in the cluster. Nodes have a TaskTracker … Seguir leyendo

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