Distributed Systems

Preview — 3 of 10 questions

What does the CAP theorem state?

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CP (Consistency + Partition Tolerance):
  → Returns error when partition occurs rather than stale data
  → Examples: HBase, Zookeeper, MongoDB (with strong consistency)

AP (Availability + Partition Tolerance):
  → Returns potentially stale data during partition
  → Examples: Cassandra, DynamoDB, CouchDB

AA distributed system can achieve Consistency, Availability, and Partition Tolerance simultaneously.

BCAP applies only to relational databases, not NoSQL systems.

CA distributed system can guarantee at most two of: Consistency, Availability, and Partition Tolerance.

DCAP theorem states that consistency is always more important than availability.

What is a CDN (Content Delivery Network) and when should you use it?

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Without CDN:
User in Tokyo → Origin server in New York → 150ms latency

With CDN:
User in Tokyo → Edge server in Tokyo → 5ms latency

AA CDN is a type of SQL database optimized for content management systems.

BA CDN is a service that automatically scales your backend servers based on traffic.

CA CDN encrypts all traffic between your server and users.

DA CDN is a distributed network of servers that delivers static assets from locations geographically close to users to reduce latency.

Why do database indexes improve query performance?

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Table scan: check row 1, 2, 3... 1,000,000 → FOUND (500ms)

AIndexes compress data so less disk space is used.

BIndexes automatically cache the results of frequent queries in memory.

CIndexes replicate data across multiple servers for redundancy.

DIndexes create a sorted data structure that allows the database to find rows without scanning the entire table.

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