Streamlining Data Ingestion with Delta Lake Autoloader

VivekR
4 min readApr 24, 2023
Auto Loader in Delta Lake. Source: element61

Autoloader is a powerful feature of Delta Lake that allows you to efficiently load data from cloud storage services such as Amazon S3, Azure Blob Storage, and Google Cloud Storage. It eliminates the need for complex ETL (Extract, Transform, Load) jobs or manual intervention to load data from cloud storage into Delta Lake tables. In the previous article, we talked about Maximizing Data Pipeline Reliability with Delta Live Table. In this article, we’ll take a deep dive into the Autoloader functionality and explore its advantages and limitations.

What is Autoloader?

Autoloader is a feature in Delta Lake that provides an easy way to automatically load data from cloud storage into Delta Lake tables. It automatically detects new data files as they appear in a cloud storage location, ingests them into Delta tables, and manages the underlying schema evolution. The Autoloader function can be configured to load data from various sources such as CSV, Parquet, JSON, and ORC. It is also capable of handling data compression codecs such as gzip, snappy, and bzip2. This makes it a flexible and powerful tool for managing large datasets.

Where is Autoloader used?

Autoloader is used in a variety of scenarios where data needs to be automatically ingested into Delta tables. It is commonly used in data ingestion pipelines, where new data files need to be loaded into Delta tables as soon as they become available. It can also be used in data lake architectures to automate the process of loading data into Delta tables from different sources. Autoloader is particularly useful in real-time analytics and IoT applications, where data is constantly being generated and needs to be ingested into Delta tables for further processing.

Advantages of Autoloader:

  1. Automated Data Ingestion: Autoloader eliminates the need for manual intervention in loading data into Delta tables. It automatically detects new data files and ingests them into Delta tables.
  2. Flexible Configuration: Autoloader can be configured to load data from different sources such as CSV, Parquet, JSON, and ORC. It also supports various data compression codecs such as gzip, snappy, and bzip2.
  3. Schema Evolution Management: Autoloader can handle schema evolution, i.e., adding or modifying the table schema when new data is ingested. This ensures that the data remains consistent and can be queried without any issues.
  4. High Performance: Autoloader is optimized for high-performance data ingestion. It uses parallelism and efficient caching mechanisms to ensure that data is ingested into Delta tables as fast as possible.

Limitations of Autoloader:

  1. Limited to Cloud Storage: Autoloader is currently only available for ingesting data from cloud storage services such as Amazon S3, Azure Blob Storage, and Google Cloud Storage. It cannot be used to load data from on-premises storage systems.
  2. Limited Data Formats: Autoloader can only load data in a limited set of formats such as CSV, Parquet, JSON, and ORC. If your data is in a different format, you will need to convert it to one of the supported formats before ingesting it into Delta tables.

Code Examples:

Here’s an example of using Autoloader to load CSV files from an S3 bucket into a Delta table:

from delta.tables import *

# Define the S3 path where the CSV files are located
input_path = "s3a://my-bucket/my-folder/*.csv"

# Define the Delta table path where the data will be ingested
output_path = "/mnt/delta/my-table"

# Define the schema of the CSV files
schema = "id INT, name STRING, age INT"

# Configure the Autoloader function
AutoLoader = DeltaTable.createOrReplaceDeltaTable(
spark, output_path
).onDataChange(
input_path=input_path,
format="csv",
schema=schema
)

# Start the Autoloader function
AutoLoader.start()

In this example, we’re using the DeltaTable.createOrReplaceDeltaTable method to create a Delta table or replace an existing one. We're then using the onDataChange method to configure the Autoloader function to ingest data from the S3 bucket in CSV format and map it to the defined schema. Finally, we're starting the Autoloader function using the start method.

Conclusion:

Autoloader is a powerful feature of Delta Lake that simplifies the process of ingesting data from cloud storage into Delta tables. It automates the data ingestion process, manages schema evolution, and provides high performance. However, it is currently limited to cloud storage and a limited set of data formats. With the advantages and limitations of Autoloader in mind, you can use this feature to streamline your data ingestion pipelines and make them more efficient.

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VivekR

Data Engineer, Big Data Enthusiast and Automation using Python