If Delta Lake Uses Immutable Files, How Do UPDATE, DELETE, and MERGE Work?

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Listen and Watch here One of the most common questions data engineers ask is: if Delta Lake stores data in immutable Parquet files, how can it support operations like UPDATE , DELETE , and MERGE ? The answer lies in Delta Lake’s transaction log and its clever file rewrite mechanism. 🔍 Immutable Files in Delta Lake Delta Lake stores data in Parquet files, which are immutable by design. This immutability ensures consistency and prevents accidental corruption. But immutability doesn’t mean data can’t change — it means changes are handled by creating new versions of files rather than editing them in place. ⚡ How UPDATE Works When you run an UPDATE statement, Delta Lake: Identifies the files containing rows that match the update condition. Reads those files and applies the update logic. Writes out new Parquet files with the updated rows. Marks the old files as removed in the transaction log. UPDATE people SET age = age + 1 WHERE country = 'India'; Result: ...
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Datawarehouse Vs Datalake

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 Data Warehouse : A data warehouse is a centralized repository that stores structured and processed data from various sources. It's optimized for querying and analysis, typically using a schema-on-write approach, where data is structured and organized before being loaded into the warehouse. Data warehouses are designed for supporting business intelligence (BI) and analytics applications, providing fast and reliable access to historical data.


Q. How do data lakes differ from data warehouses, and what are their primary characteristics?

Unlike data warehouses, data lakes store raw, unstructured, or semi-structured data in its native format. They use a schema-on-read approach, where data is ingested without prior structuring, allowing for flexible exploration and analysis. 

Data lakes are designed to store vast amounts of data at a low cost and support a wide range of data processing and analytics use cases, including data exploration, machine learning, and advanced analytics.

Q. What are some factors to consider when deciding between these two architectures?

I would recommend leveraging a data lake architecture but with specific enhancements to address both real-time analytics and ad-hoc exploration effectively.

  1. Flexibility and Scalability:
    A data lake provides the flexibility to store raw, semi-structured, and unstructured data without requiring upfront schema definitions. This is crucial for handling diverse data sources and formats, enabling quick data ingestion and experimentation.

  2. Support for Real-Time Analytics:
    Technologies like Apache Spark, Apache Flink, or Kafka Streams can be integrated with a data lake to process and analyze streaming data in real time. These tools allow for low-latency analytics on data as it arrives.

  3. Ad-Hoc Exploration:
    Since data lakes support storing raw data, data scientists and analysts can explore and experiment with raw datasets using tools like Databricks, Jupyter Notebooks, or Athena.

  4. Enhancing Query Performance:
    To optimize query performance for real-time and ad-hoc use cases, the company could implement a data lakehouse architecture. A lakehouse combines the flexibility of data lakes with the structured querying capabilities of data warehouses, using technologies like Delta Lake, Iceberg, or Hudi.

  5. Governance and Data Management:
    While data lakes are flexible, they require robust governance and metadata management (e.g., using a catalog like AWS Glue or Apache Hive) to ensure data quality and prevent the "data swamp" problem.

Why Not a Data Warehouse?

While data warehouses excel in structured query performance and predefined analytics, their rigid schema requirements and higher costs for real-time and ad-hoc workloads make them less suitable for this scenario. However, if the company prioritizes specific, well-defined reporting requirements alongside real-time analytics, a hybrid approach (e.g., combining a data lake and a warehouse) could be considered.

Conclusion:

A data lake, possibly enhanced with lakehouse features, is the optimal choice for supporting both real-time analytics and ad-hoc exploration of raw data in this scenario. It provides the required flexibility, scalability, and support for diverse workloads while enabling the organization to adapt to evolving data requirements.




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