Power of two
Latency numbers every programmer should know
Availability numbers
Example
Assumptions:
- 300 million monthly active users.
- 50% of users use Twitter daily.
- Users post 2 tweets per day on average.
- 10% of tweets contain media.
- Data is stored for 5 years.
Estimations:
Query per second (QPS) estimate:
- Daily active users (DAU) = 300 million * 50% = 150 million
- Tweets QPS = 150 million * 2 tweets / 24 hour / 3600 seconds = ~3500
- Peek QPS = 2 * QPS = ~7000
We will only estimate media storage here.
- Average tweet size:
- tweet_ id 64 bytes
- text 140 bytes
- media 1 MB
- Media storage: 150 million * 2 * 10% * 1 MB = 30 TB per day
- 5-year media storage: 30 TB * 365 * 5 = ~55 PB
Commonly asked estinations:
- QPS
- peak QPS
- storage
- cache
- number of servers
- etc