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Zero-Rename Writes in ElasticMapReduce Hive

Suthan Phillips, et al, show off some updates to the way Hive transactions commit in AWS’s ElasticMapReduce:

Our customers use Apache Hive on Amazon EMR for large-scale data analytics and extract, transform, and load (ETL) jobs. Amazon EMR Hive uses Apache Tez as the default job execution engine, which creates Directed Acyclic Graphs (DAGs) to process data. Each DAG can contain multiple vertices from which tasks are created to run the application in parallel. Their final output is written to Amazon Simple Storage Service (Amazon S3).

Hive initially writes data to staging directories and then move it to the final location after a series of rename operations. This design of Hive renames supports task failure recovery, such as rescheduling the failed task with another attempt, running speculative execution, and recovering from a failed job attempt. These move and rename operations don’t have a significant performance impact in HDFS because it’s only a metadata operation when compared to Amazon S3 where the performance can degrade significantly based on the number of files written.

This post discusses the new optimized committer for Hive in Amazon EMR and also highlights its impressive performance by running a TPCx-BB performance benchmark and comparing it with the Hive default commit logic.

Read on for a description of how commit operations work in general and how the updated Hive committer can help with certain types of queries.