Optimizing Read Performance for Multiple Small Parquet Files in S3 with PySpark

What will you learn?

In this comprehensive guide, you will delve into advanced strategies to efficiently handle over 500,000 small parquet files stored in Amazon S3 using PySpark. By implementing optimization techniques, you will significantly enhance your data processing efficiency and reduce job execution times.

Introduction to the Problem and Solution

Working with a vast number of small files in Amazon S3, such as half a million parquet files, can lead to slower-than-expected PySpark job execution. This slowdown primarily stems from the overhead associated with reading numerous small files individually. To address this challenge effectively, we will explore approaches like consolidating small files into larger ones before processing, maximizing Spark’s parallelism capabilities, and fine-tuning Hadoop configurations to optimize S3 access patterns.

Our solution revolves around minimizing read operations by aggregating smaller files into fewer larger ones and adjusting configuration settings for improved synergy between Spark and the underlying file system (S3). By incorporating these strategies, our goal is to significantly reduce job execution duration while maintaining or even enhancing data processing efficiency.


from pyspark.sql import SparkSession

# Initialize SparkSession with optimized configurations for reading from S3
spark = SparkSession.builder \
    .appName("OptimizeS3Reads") \
    .config("spark.hadoop.mapreduce.fileoutputcommitter.algorithm.version", "2") \
    .config("spark.speculation", "false") \

# Adjust Hadoop configurations specific to s3a for enhanced performance
hadoopConf = spark._jsc.hadoopConfiguration()
hadoopConf.set("fs.s3a.fast.upload", "true")
hadoopConf.set("fs.s3a.path.style.access", "true")
hadoopConf.set("fs.s3a.block.size", "256M")

# Example demonstrating consolidated reads instead of individual file reads
df = spark.read.parquet("s3a://your-bucket/path/to/consolidated/files/")

# Processing logic implementation...

# Save processed data back into larger parquet files if needed 

# Copyright PHD


The provided code showcases adjustments in both PySpark session initialization and HDFS configuration tailored for efficient access to a large volume of small parquet files stored in AWS S3. Key highlights include:

  • Optimized File Output Committer Algorithm: Setting mapreduce.fileoutputcommitter.algorithm.version as 2 minimizes communication between Spark and S3 during job commits.

  • Disabling Speculation: Turning off speculation (spark.speculation) prevents redundant tasks that could increase unnecessary read operations.

  • Improved Uploading Mechanisms & Block Sizes: Configurations like fast upload for s3a enhance write performance back to S3 by utilizing memory buffers effectively; increasing block size reduces overhead linked with managing multiple smaller blocks.

By consolidating smaller input files into larger logical units before reading them (df = spark.read.parquet(…)), I/O overhead is significantly reduced. Furthermore, outputting processed data into fewer but larger parquet files enhances the efficiency of subsequent read operations.

  1. How does consolidating small parquet files improve performance?

  2. Consolidation reduces the overhead associated with opening each file individually, thereby speeding up overall read times.

  3. Can these optimizations compromise data integrity?

  4. No, these optimizations focus on how data is accessed rather than altering content itself, ensuring maintained data integrity throughout.

  5. Why disable task speculation?

  6. Disabling task speculation prevents unnecessary duplication of effort when dealing with many small file accesses where setup costs dominate actual computation time. This ensures optimal resource utilization without introducing redundant workloads unnecessarily.

  7. Is there any cost implication for these optimizations?

  8. There may be minor cost implications related mostly to storage due to consolidation resulting in increased sizes. However, gains in enhanced processing speeds generally offset these expenses, making optimizations a worthwhile pursuit.

  9. How does changing block size affect performance?

  10. Increasing block size allows the system to handle larger chunks at once, reducing total network requests made and leading to faster reads/writes due to operational efficiencies gained during the process.


Efficiently managing numerous small parquet files on AWS S3 via PySpark involves a multifaceted strategy focusing on consolidation and fine-tuning various configuration parameters within your environment. By implementing the recommended optimizations outlined above, you can expect significant improvements in both execution times and resource utilization efficiency during big data processing tasks. It is essential to test different configurations tailored specifically to your use case to identify the optimal set-up that aligns best with your business objectives and goals.

Credits: PythonHelpDesk.com

Tags: PySpark, Optimization, AWS S3, Parquet Files

Leave a Comment