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This is a hard difficulty System Design question, commonly asked during HR Screen rounds at Databricks.

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This question is commonly asked for Software Engineer candidates at Databricks during technical interviews.

Design concurrent range-aware file caching client

Quick Overview

This question evaluates understanding of concurrent, range-aware client-side file caching—covering concurrency control and deduplication of in-flight requests, chunking and prefetch strategies, persistence, eviction policies, validation, and reliability—and is categorized under System Design.

System Design: High-throughput Client-side Ranged-read File Cache

You are asked to design and specify a client-side cache that accelerates ranged reads against a remote storage service.

Context and Assumptions

The remote service supports HTTP Range-like reads: fetch(filename, offset, length).
There is also an API to download an entire file by filename and known size.
Workloads consist of many concurrent ranged reads, often overlapping or adjacent.
The cache persists on local disk across process restarts.

Requirements

Concurrency and coalescing
- Efficiently handle concurrent requests for overlapping/adjacent ranges.
- Deduplicate overlapping in-flight downloads so only one fetch per chunk occurs.
- Provide thread-safe access and correctness under concurrency.
Chunking, request strategy, and prefetch
- Choose chunk size and justify trade-offs.
- Coalesce requests to reduce remote calls and over-fetch sensibly.
- Implement prefetch/read-ahead strategies for sequential access.
Backpressure and rate limiting
- Limit remote QPS/throughput and disk I/O concurrency.
- Disable prefetch under load; bound queues.
Cache management
- Cache indexing and lookup.
- Eviction policy (e.g., LRU) with byte budget.
- Persistence across restarts.
- Validation and invalidation if the remote file changes.
Reliability
- Handle partial failures, retries, and timeouts.
- Resume or refetch partial chunks.
API semantics
- Define read(filename, offset, length) (sync or async), and streaming semantics if applicable.
- Define write policy (e.g., read-through only, or write-through with invalidation).
Deliverables
- Describe key data structures and on-disk layout.
- Provide pseudocode for coordinating fetch, cache lookup, coalescing, and concurrency control.
- Analyze scalability, correctness under concurrency, and time/space complexity.

Quick Overview

Context and Assumptions

The remote service supports HTTP Range-like reads: fetch(filename, offset, length).

There is also an API to download an entire file by filename and known size.

Workloads consist of many concurrent ranged reads, often overlapping or adjacent.

The cache persists on local disk across process restarts.

Requirements

Concurrency and coalescing

Efficiently handle concurrent requests for overlapping/adjacent ranges.
Deduplicate overlapping in-flight downloads so only one fetch per chunk occurs.
Provide thread-safe access and correctness under concurrency.

Chunking, request strategy, and prefetch

Choose chunk size and justify trade-offs.
Coalesce requests to reduce remote calls and over-fetch sensibly.
Implement prefetch/read-ahead strategies for sequential access.

Backpressure and rate limiting

Limit remote QPS/throughput and disk I/O concurrency.
Disable prefetch under load; bound queues.

Cache management

Cache indexing and lookup.
Eviction policy (e.g., LRU) with byte budget.
Persistence across restarts.
Validation and invalidation if the remote file changes.

Reliability

Handle partial failures, retries, and timeouts.
Resume or refetch partial chunks.

API semantics

Define read(filename, offset, length) (sync or async), and streaming semantics if applicable.
Define write policy (e.g., read-through only, or write-through with invalidation).

Deliverables

Describe key data structures and on-disk layout.
Provide pseudocode for coordinating fetch, cache lookup, coalescing, and concurrency control.
Analyze scalability, correctness under concurrency, and time/space complexity.

Design concurrent range-aware file caching client

Quick Overview

System Design: High-throughput Client-side Ranged-read File Cache

Context and Assumptions

Requirements

Solution

Comments (0)

Design concurrent range-aware file caching client

Quick Overview

System Design: High-throughput Client-side Ranged-read File Cache

Context and Assumptions

Requirements

Solution

Comments (0)