Coinbase Backend Engineer System Design Questions

Coinbase needs a reliable way to queue messages between its services for processing operations asynchronously.
Design a MessageQueue class that allows adding messages, retrieving the next message, and checking the size of the queue.
Class signature:
- class MessageQueue:
- def enqueue(message: str) -> None – Adds a message to the queue.
- def dequeue() -> str – Retrieves and removes the next message from the queue.
- def size() -> int – Returns the current size of the queue.
Example 1:
Input: enqueue('msg1')
Output: None
Explanation: Message is queued.Example 2:
Input: size()
Output: 1
Explanation: Queue size is currently 1 message.
Constraints:
- 1 <= len(message) <= 100

Coinbase requires a robust job scheduler to execute tasks at specific intervals. The system must handle thousands of jobs simultaneously.
Design a JobScheduler class that schedules jobs to run after a defined interval. It should allow for adding, removing, and checking job status.
Class signature:
- class JobScheduler:
- def add_job(job_id: str, interval: int) -> None – Adds a job with a specified interval (in seconds).
- def remove_job(job_id: str) -> None – Removes a job from the scheduler.
- def get_status(job_id: str) -> str – Returns the current status of a job (e.g. 'running', 'pending', 'completed').
Example 1:
Input: add_job('job1', 5)
Output: None
Explanation: Job is scheduled.Example 2:
Input: get_status('job1')
Output: 'pending'
Explanation: Job is pending execution.
Constraints:
- 1 <= interval <= 3600
- 1 <= len(job_id) <= 20