Question 1440

Six Hundred Eighty Nine

Your fan-out workers each sustain 9,000 timeline inserts per second. Product says a post must be in every follower's timeline within 5 seconds. An account with 31,000,000 followers posts.

How many workers must be free at that instant to hold the 5 second promise for that single post?

A

6,889, from ⌈31,000,0009,000×2⌉\lceil \frac{31{,}000{,}000}{9{,}000} \times 2 \rceil, doubling for the replica write

B

689, from ⌈31,000,0009,000×5⌉\lceil \frac{31{,}000{,}000}{9{,}000 \times 5} \rceil, which is why nobody pushes for accounts at this scale

C

3,445, from ⌈31,000,0009,000⌉\lceil \frac{31{,}000{,}000}{9{,}000} \rceil, the workers needed to finish in one second

D

12, from ⌈31,000,0009,000×300⌉\lceil \frac{31{,}000{,}000}{9{,}000 \times 300} \rceil, reading the promise as five minutes rather than five seconds