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While this loads — quick one
Every subscriber must get each event. A queue, or pub/sub?
Message queueorPub/Sub
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While this loads — quick one
Every subscriber must get each event. A queue, or pub/sub?
Loading the challenge…
While this loads — quick one
Every subscriber must get each event. A queue, or pub/sub?
A messaging app lets people chat one-to-one and in small groups from their phones. A message sent to someone who has the app open should arrive within a fraction of a second, without their phone repeatedly asking the server whether anything is new. Hundreds of thousands of people are connected at any moment, spread across many servers. When the recipient's app is closed, the message must still reach them: their phone should get an alert, and the message must be waiting when they open the app, even days later. Messages arrive in enormous volume, are almost never edited, and are always read one conversation at a time, newest first.
Every system design question opens with an account. Your design is scored the same way every time, with the reason behind each requirement, and your attempts are kept so you can see what you found hard.