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Capacity Estimation

Assume:

  1. DAU = 1 B users
  2. MAU = 2 B users

A. Throughput [requests per unit of time]​

Throughput can be further divided into write-throughput and read-throughput.

So, Let's start with what all operations user can perform:

  1. Send a message [Write-Operation]
  2. Message Status change from Sent to Delivered to Seen [Write-Operation]
  3. User status change from Last-Seen to Online [Write-operation]
  4. Reciever Reads the message [Read-Operation]
  5. Sender reads the message-status or user-status [Read-Operation]

A.1 Write-Throughput​

Assume Each user will send 10 messages daily on an average. Also Assume, Each user stays on an average of 30 minutes on the app, and last-seen is checked every minute.

Total Message-Write operations per day = DAU * 10 = 1 B * 10 = 10B write requests per day
Total Message-status-change per day = (Total-Messages) * (Total states [Sent, Delievered, Read]) = 10B * 3 = 30B message-status write-request per day
Total last-seen-writes per day = DAU * 30 = 30B last-seen writes per day

A.2: Read-Throughput​

Assume every user read each message delivered.

Total Message Read operations per day = Total Messages = 10 B read-request per day.

Note: In read-throughput, not covering the last-seen-reads and message-status-change-reads, Since those operations resource-usage is very less compared to reading a whole new message

B. Storage [Bytes per unit of time]​

Assume Average storage as = Size of Long-Url + Size of Short-Url + Metadata like timestamp = 100bytes + 30 bytes + 70 bytes = 200 bytes.

Average Mapping-Size = 200 b
Total Storage per day  = Write-throughput * Average Content-Size
                        = 150M * 200 b
                        = 30 M Kb
                        = 30 Gb per day

Storage for 10 years = 30 Gb * 365 * 10
                     = 109500 Gb
                     = 0.1095 Pb

C. Cache-Memory​

Cache Memory is generally 1% of total storage per day

Cache-Memory = 1% of daily Storage = 0.01 * 30 Gb = 3 Gb per day

D. Network Bandwidth​

D.1: Ingress Traffic​

Traffic coming into the system i.e. write traffic

Ingress = Write per second
        = (Total Writing requests per second) * (Average Entry size)
        = (150M / 24/ 60/ 60) *  (200 b)
        = (1.73 K requests/sec) * (200 b)
        = 346 Kbps

D.2: Egress Traffic​

Traffic going out of the system i.e. read traffic

Egress = read per second
        = (Total read requests per second) * (Average Entry Size)
        = (6B / 24/ 60/ 60) *  (200 b)
        = (6.44 K/sec) * (200 b)
        = 13.8 Mbps