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System Design Basics for Backend Developers · Lesson

Database Connection Pooling

Learn how connection pools eliminate the overhead of opening database connections per request, and how to size and tune a pool for performance.

The Cost of a Connection

Opening a database connection is expensive: a TCP handshake, authentication, and session setup can take tens of milliseconds. Doing this on every request adds latency and load you do not need.

What a Connection Pool Is

A connection pool keeps a set of open connections ready to reuse. A request borrows one, runs its query, and returns it — no setup cost per request.

  • Lower latency
  • Less load on the database
  • A natural cap on concurrent connections

All lessons in this course

  1. Latency & Throughput Optimization
  2. Concurrency & Parallelism
  3. Performance Testing & Profiling
  4. Database Connection Pooling
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