Apply Amdahl's Law to web application bottlenecks. Speedup = 1 / (S + (1-S)/N), where S is the non-scalable fraction (e.g., database writes). A 10% serial DB write fraction caps scaling at 10× regardless of servers.
Enter the values for the scenario you are assessing. Apply Amdahl's Law to web application bottlenecks. Speedup = 1 / (S + (1-S)/N), where S is the non-scalable fraction (e.g., database writes). A 10% serial DB write fraction caps scaling at 10× regardless of servers. Use the amdahl's law (web scaling) result to inform your calculation.