Slack Message Storage & QPS

Medium

Slack has 20 million DAU, each sending 5 messages/day. A message row with metadata is ~2 KB. Messages are retained forever.

Use: 1 day = 86,400 sec ≈ 10^5 sec. Powers of 10: 1 KB = 10^3 B, 1 MB = 10^6 B, 1 GB = 10^9 B, 1 TB = 10^12 B, 1 PB = 10^15 B.

Compute daily volume, write QPS, peak QPS, and one year of message storage.

Back-of-envelope counts: any answer within ±30% of the target is correct, just like a real interview. Suffixes like k, M, B work.