Performance

The constant factors that dominate asymptotics in practice, and cache-oblivious algorithms as the theoretical response.

The unimplementable best cache policy, and the proof that LRU is k-competitive with it. The application of Competitive analysis and ski rental, so it follows it.

Rate limiting has a theory: bound the arrival curve and you get a provable bound on delay and queue depth.

The M/M/1 queue's 1/(1-rho) blowup. Why a service at 80% load is fine and at 95% is on fire.

L = lambda W, with essentially no assumptions. Capacity planning from one line of algebra.

A randomized scheduler with a provable bound on both time and space, and why every modern runtime converged on it.

Random placement gives max load ~log n / log log n; picking the emptier of two random bins collapses it to log log n.

Amdahl's rebuttal, and then the law that adds a negative term for coordination: past a point, more nodes make it slower.

The serial fraction caps your speedup, brutally. Pure algebra, not an observed regularity — the empirical part of the speedup story belongs to Gustafson's law and...