HLD:Lecture 1: performance of a system | High Level Design | MAANGs

In this lecture, we dive into cache coherence, the volatile keyword, and memory visibility—essential concepts in multithreading, concurrency control, and system performance optimization. If you are a Java/C++ developer, backend engineer, or preparing for FAANG-level interviews, understanding these concepts is critical for writing thread-safe, high-performance code

Why Are These Concepts Important?
Modern CPUs use multiple cores, each with its own cache, to speed up computation. While this improves performance, it introduces consistency issues in multi-threaded programs. Without proper synchronization, threads might read stale data, leading to subtle, hard-to-detect bugs. This lecture explains why this happens and how to fix it.

What You’ll Learn in This Video:

Cache Coherence Basics:

Why CPU caches can cause stale reads in multi-core systems.

Hardware protocols like MESI (Modified, Exclusive, Shared, Invalid) ensuring coherence.

The difference between cache coherence and memory consistency models.

Memory Visibility & Reordering:

How compilers and CPUs reorder instructions for optimization.

Why instruction reordering can break multithreaded programs.

The volatile Keyword in Java/C++:

What volatile does and does not guarantee.

How it prevents read/write reordering and ensures visibility across threads.

Why volatile is not a replacement for locks.

Happens-Before Relationships & Memory Barriers:

How modern languages (Java Memory Model, C++11 Memory Model) define thread-safe execution.

The role of fences/barriers in enforcing ordering.

Use Cases & Interview Questions:

Implementing singleton patterns with volatile.

Solving double-checked locking issues.

Real-world concurrency bugs caused by missing visibility guarantees.

Why Watch This Lecture?

Gain a deep understanding of low-level concurrency issues.

Learn how volatile interacts with CPU caches and memory models.

Be ready for system design and multithreading interview questions.