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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Optimize Azure Storage Costs with Smart Tier — A Complete Guide to Microsoft’s Automated Tiering Feature

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Smart Tier for Azure Blob & Data Lake Storage — A Smarter, Cost-Efficient Way to Manage Your Data


Microsoft has introduced Smart Tier (Public Preview), a powerful automated data-tiering feature for Azure Blob Storage and Azure Data Lake Storage. This feature intelligently moves data between the hot, cool, and cold access tiers based on real-world usage patterns—no manual policies, rules, or lifecycle setups required.

🔥 What is Smart Tier?

Smart Tier automatically analyzes your blob access patterns and moves data to the most cost-efficient tier. It eliminates guesswork and minimizes the need for administrators to manually configure and adjust lifecycle management rules.

✨ Key Benefits

  • Automatic tiering based on access patterns
  • No lifecycle rules or policies required
  • Instant promotion to hot tier when data is accessed
  • Cost-efficient storage for unpredictable workloads
  • No early deletion fees for tier transitions

🔄 How Smart Tier Works

Smart Tier continuously monitors access patterns and dynamically places data in the appropriate tier:

  • Day 0: New data is stored in the Hot tier.
  • After 30 days of inactivity: Data automatically moves to the Cool tier.
  • After 90 days of inactivity: Data transitions to the Cold tier.
  • If accessed at any time: The object is instantly moved back to the Hot tier and restarts the cycle.

This automated behavior ensures optimal costs over time while maintaining performance and availability.

📌 Important Details

  • Only Block Blobs are supported (not Append or Page blobs).
  • Small blobs under 128 KiB remain in the Hot tier and are not tiered.
  • Smart Tier does not support Archive tier transitions.
  • Monitoring costs apply per 10,000 objects, but tier transitions themselves are free.
  • Access charges are billed at Hot tier rates since data is promoted on access.

💼 When Should You Use Smart Tier?

Smart Tier is ideal if:

  • Your data access patterns are unpredictable or inconsistent.
  • You want a set-it-and-forget-it storage optimization method.
  • You prefer to avoid managing complex lifecycle rules.
  • You want to minimize storage costs over the long term.

⚙️ Enabling Smart Tier

You can enable Smart Tier at the storage account level for supported redundancy types. Once enabled:

  • All blobs without explicit access tiers will be managed by Smart Tier.
  • Blobs with manually assigned tiers stay where they are.

📘 Learn More

For full technical details and the latest updates, visit the official Microsoft documentation:
Optimize Azure Blob Storage costs with Smart Tier (Public Preview)

💡 Final Thoughts

Smart Tier is a significant step toward fully automated, intelligent cloud storage management. If you're dealing with unpredictable access patterns or want to simplify your storage operations while reducing costs, Smart Tier is a powerful feature worth adopting.

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