Upgrading from Azure Blob Storage to Azure Data Lake Storage? – Beware of Python Pitfalls!

Introduction

Upgrading your Azure Blob Storage account to Azure Data Lake Storage (ADLS) Gen2 unlocks powerful capabilities that can significantly enhance your storage performance, management, and analytics workflows. ADLS Gen2 enables hierarchical namespaces (HNS), which introduce file and directory-level operations, similar to a traditional file system.

Here are some key benefits you’ll get when upgrading to ADLS Gen2:

1. Higher throughput, IOPS (input/output operations per second), and storage capacity limits.
2. Faster operations, such as rename and delete operations, because you can operate on individual node URIs (no need for copying and deleting blobs).
3. An efficient query engine that transfers only the necessary data.
4. Granular security controls at the container, directory, and file levels.

However, with these improvements come differences in Python APIs that can lead to potential pitfalls. This article will guide you through these differences with code snippets to ensure a smooth transition.

For full migration guidance, visit Microsoft Docs.

Directories and Blob Listings: The Flat vs. Hierarchical Namespace

In Azure Blob Storage (without HNS), blobs are listed in a flat structure where folder paths are part of the blob name. In ADLS Gen2 (with HNS enabled), directories are independent entities that can contain blobs or be empty.

Documentation Recap

Flat Namespace (Blob Storage): Virtual directories exist as part of the blob name (e.g., "folder1/file.txt").

Hierarchical Namespace (ADLS Gen2): Directories exist as real objects. Listing blobs returns both directories and blobs distinctly.

Python Code Examples

Differences in Directory and Metadata Handling

Upload and Directory Creation Differences

Efficient Rename Operations

In ADLS Gen2, renaming a blob is an instant operation that doesn’t require a copy-delete cycle.

In contrast, Blob Storage requires copying the blob to a new location and deleting the original blob.

Note: The blob’s last modified time remains unchanged since its contents are unaffected.

List Order Differences

Blob Storage: Lists blobs in lexicographical order.

ADLS Gen2: Lists directories and blobs using a depth-first search order.

Takeaways

1. Use walk_blobs() instead of list_blobs() to handle directories and blobs separately in ADLS Gen2.
2. Deleting a directory in ADLS Gen2 also deletes all files under that directory.
3. Take advantage of instant rename operations in ADLS Gen2 to improve performance.

For a detailed migration guide, visit the Microsoft Docs.

By addressing these differences, you can ensure that your Python applications make the most of ADLS Gen2 features while avoiding common pitfalls.