Apache Hudi Explained: Managing Streaming Data in Data Lakes

Written By:
Founder & CTO
June 24, 2025

As organizations move toward data-driven decision making, the need for processing and analyzing real-time data in a scalable, consistent, and cost-effective way has become a central challenge. Modern data systems increasingly rely on data lakes to store vast amounts of structured, semi-structured, and unstructured data, but traditional data lakes fall short when it comes to handling fast-moving, continuously generated streaming data. Enter Apache Hudi, an open-source data lake framework designed to bring streaming, transactional capabilities to data lakes without the bloat of traditional data warehouse solutions.

In this deep-dive, we’ll explore what makes Apache Hudi a game-changer for developers and data engineers working with modern data lake architectures, how it simplifies incremental processing, enables upserts and deletes at scale, and why it is a cornerstone technology for anyone managing streaming data pipelines.

What Is Apache Hudi and Why It Matters to Developers

Apache Hudi, short for Hadoop Upserts Deletes and Incrementals, is a data lake storage framework that enables streaming ingestion, incremental processing, and ACID transactions in cloud-native data lakes. Created by Uber to address the limitations of existing data lake tools, Hudi brings database-like operations such as inserts, updates, deletes, and time travel directly to data lakes built on cloud object stores like Amazon S3, Google Cloud Storage, and Azure Data Lake.

Why Developers Should Care About Apache Hudi

Traditionally, data lakes were optimized for append-only batch jobs. Developers would run large ETL processes overnight to load fresh data, with little or no support for handling late-arriving data, partial updates, or deletions. This resulted in brittle, complex, and slow pipelines. With Apache Hudi, you get:

  • Upserts and Deletes: Update and delete individual records in-place.

  • Incremental Queries: Consume only new or changed records.

  • Transactional Guarantees: ACID compliance even on object stores.

  • Real-Time Analytics: Near-instant visibility into ingested data.

This allows developers to build modern data pipelines that are agile, resilient, and scalable without resorting to heavyweight, monolithic solutions.

Streaming Data Lake Platform: Core Hudi Features
Streaming Ingestion with DeltaStreamer and CDC Sources

Apache Hudi supports streaming ingestion using tools like DeltaStreamer, a lightweight ingestion service that allows you to continuously load data from various sources such as Kafka, Debezium, MySQL, or file systems. Unlike batch jobs that require manual scheduling, DeltaStreamer can operate in continuous mode, ingesting data in real time and writing it directly into Hudi-managed tables.

Developers can build end-to-end streaming data pipelines where new events are captured, transformed, and landed in data lakes with sub-minute latency. This is crucial for real-time applications such as:

  • Fraud detection

  • Live dashboards

  • Recommendation engines

  • Operational analytics

The support for Change Data Capture (CDC) means that Hudi can work seamlessly with systems like Debezium, which track changes in source databases, making it a robust choice for database replication, audit trails, and data synchronization scenarios.

Merge-On-Read (MoR) and Copy-On-Write (CoW): Write Modes Explained

Apache Hudi offers two powerful table types that developers can choose based on workload needs:

  • Copy-On-Write (CoW): All changes (inserts, updates, deletes) result in new Parquet files being written. Ideal for analytical queries that need high read performance.

  • Merge-On-Read (MoR): Writes updates to delta logs in Avro format and merges them on read. Best suited for high-frequency updates or streaming ingestion.

This flexibility allows developers to optimize for write throughput or read performance depending on the use case. For example, a user behavior tracking system may prefer MoR to support high update frequency, while a BI dashboard may benefit from CoW for faster reads.

ACID Transactions and Snapshot Isolation

Apache Hudi brings ACID transaction support to cloud object storage, a feat previously reserved for databases and data warehouses. This means that all operations are atomic, consistent, isolated, and durable. When writing to a Hudi table, each commit is recorded in a timeline that guarantees isolation between reads and writes.

This is particularly helpful in environments where multiple writers and readers are active at the same time. With snapshot isolation, a query will always see a consistent view of the data, even if other updates are happening concurrently in the background.

For developers, this translates to:

  • No partial data reads

  • Safe concurrent access

  • Reliable rollback mechanisms

Key Developer Benefits of Apache Hudi
Real-Time Analytics and Fresh Data

In traditional pipelines, data might not be available for hours or even a day after it’s generated. Apache Hudi changes that by allowing streaming ingestion with commit-level visibility, meaning new data is queryable within seconds or minutes of arrival.

This is a boon for real-time analytics where businesses rely on up-to-date metrics, such as:

  • User activity trends

  • Inventory levels

  • Payment processing statuses

Developers can use tools like Apache Spark, Presto, Hive, or Trino to run snapshot queries that return consistent results from Hudi-managed tables, even as new data is continuously being ingested.

Incremental Processing and Efficiency

One of the most powerful aspects of Apache Hudi is its incremental query capability. Instead of reprocessing an entire dataset, developers can query for only the new or changed data since the last checkpoint. This reduces compute costs, shortens pipeline run times, and enhances scalability.

Imagine running daily aggregations on terabytes of logs. Instead of re-scanning the entire dataset, Apache Hudi allows you to fetch just the latest changes and process only those, dramatically increasing throughput and reducing cost.

Schema Evolution and Metadata Management

Apache Hudi uses Avro schemas and maintains rich metadata for all files, records, and operations. This enables schema evolution without breaking downstream pipelines. Developers can:

  • Add new fields to records

  • Track schema versions

  • Validate compatibility during ingestion

This makes it easy to maintain data quality and consistency as applications evolve, ensuring that data lakes remain resilient to change and developer-friendly.

Time Travel, Rollbacks, and Data Governance

Hudi maintains a full commit timeline, recording every write operation to the data lake. Developers can use this timeline to:

  • Query historical versions of a dataset (time travel)

  • Roll back faulty commits

  • Trace the origin of data issues

This is essential for data governance, compliance, and debugging. A developer can inspect when a particular record was changed, what values it had previously, and who made the change, all within the data lake, using standard query engines.

File Indexing and Partition Pruning

To speed up queries and write operations, Hudi includes record-level indexing and partition pruning. This means developers can write upserts and deletes efficiently by avoiding full table scans. Instead, Hudi can quickly locate the file group where a record resides, minimizing I/O and latency.

In scenarios involving billions of rows, this optimization is vital for maintaining performance and responsiveness.

How to Use Apache Hudi: Developer Workflow
Defining a Table and Schema

A Hudi table begins with defining key attributes such as:

  • Record key: Uniquely identifies each row.

  • Pre-combine key: Determines the latest version of a record.

  • Partition path: Controls data layout (e.g., dt=2025-06-23).

Developers define this schema using Avro or JSON, along with configurations for cleaning, compaction, and indexing. This schema-first approach encourages clarity, consistency, and extensibility in data pipelines.

Building Ingestion Pipelines

Data ingestion can be done through:

  • Apache Spark jobs using Hudi APIs

  • Hudi’s DeltaStreamer

  • Apache Flink for streaming writes

  • Kafka and Debezium for CDC ingestion

Each method gives developers fine-grained control over data transformations, validation, and output formats. You can ingest in near real-time, batch mode, or hybrid workflows depending on your operational needs.

Querying the Data

Once data is ingested, querying becomes seamless. Developers can use:

  • Snapshot queries: Return the latest view of the dataset.

  • Incremental queries: Return only changed records since a given commit time.

  • Point-in-time queries: Return the state of the dataset as of a particular commit.

These queries are supported by engines like Spark SQL, Trino, Hive, and Presto. You can even use AWS Athena or BigQuery with Hudi-compatible formats, making it a versatile choice for hybrid cloud ecosystems.

Managing Data Lifecycle

Apache Hudi supports lifecycle operations such as:

  • Compaction: Merges delta files for faster reads.

  • Clustering: Rewrites data layout for improved partitioning.

  • Cleaning: Removes obsolete file versions to save storage.

  • Archival: Moves older commits to long-term storage for compliance.

These operations ensure that your data lake remains fast, cost-efficient, and scalable even as the data grows.

Apache Hudi vs Traditional Approaches: A Paradigm Shift

In traditional data lake systems:

  • Updates require full reprocessing.

  • Deletes involve rewriting entire partitions.

  • ACID compliance is non-existent.

  • Time travel or rollback is unsupported.

With Apache Hudi:

  • Updates and deletes are first-class citizens.

  • Only new data is processed incrementally.

  • Transactions are consistent and isolated.

  • Historical queries and rollback are simple and fast.

This shift allows developers to treat the data lake like a database, reducing complexity while increasing flexibility.

Real-World Use Cases and Production Deployments

Apache Hudi is already powering production systems at scale:

  • Uber uses Hudi to ingest and manage over hundreds of terabytes daily across multiple teams and services.

  • Robinhood uses CDC + Hudi pipelines for consistent ingestion into data lakes.

  • Walmart, GE Aviation, and Netflix are also known to leverage Hudi for real-time analytics and scalable ingestion.

These implementations validate Hudi’s maturity and versatility in the enterprise data ecosystem.

Best Practices for Developers Using Apache Hudi
  1. Choose MoR vs CoW wisely based on update frequency.

  2. Enable incremental pull mechanisms to boost pipeline efficiency.

  3. Regularly schedule compaction and clustering for optimal query speed.

  4. Implement schema validation in CI/CD pipelines.

  5. Monitor commit timelines and configure appropriate retention policies.

  6. Optimize indexing strategies based on record volume and write pattern.

  7. Leverage DeltaStreamer for managed CDC ingestion at scale.

  8. Keep partitioning strategies simple and aligned with query patterns.

Why Apache Hudi Is the Future of Data Lakes for Developers

Apache Hudi allows developers to transform passive data lakes into active data platforms. With support for real-time ingestion, ACID transactions, scalable indexing, and full query support, it redefines what’s possible in open data architecture. Whether you're a data engineer, ML engineer, or analytics developer, Apache Hudi provides the building blocks to create low-latency, resilient, and auditable data pipelines that work at petabyte scale.