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What is Databricks Auto Loader, and how does it handle new files?

Spark/Big Dataeasy0.4 min readPremium

**Auto Loader**: Incremental file ingestion from cloud storage. Detects new files; processes only new; checkpoint for exactly-once. **How**: (1) Directory listing or cloud notifications (S3 Events, etc.) to detect new files. (2) Checkpoint tracks processed files. (3) Schema...

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Frequency
Low
Asked at 1 company
Category
452
questions in Spark/Big Data
Difficulty Split
88E|81M|283H
in this category
Total Bank
1,863
across 7 categories
Asked at these companies
TCS

Why This Question Matters

This easy-level Spark/Big Data question appears frequently in data engineering interviews at companies like TCS. While less common, it tests deeper understanding that distinguishes strong candidates.

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Expert Answer
84 words

Auto Loader: Incremental file ingestion from cloud storage. Detects new files; processes only new; checkpoint for exactly-once.

How: (1) Directory listing or cloud notifications (S3 Events, etc.) to detect new files. (2) Checkpoint tracks processed files. (3) Schema evolution optional. (4) Trigger: once, availableNow, or continuous.

Why vs. Batch Read: Batch rereads all; Auto Loader incremental. At 1M files/day, batch is infeasible.

Scalability Trade-offs: Notifications scale; listing doesn't. Provide schema when static.

Cost Implications: Notifications cheaper than LIST at scale. Checkpoint in durable storage.

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