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Learn Queues

Queues buffer work. At-least-once delivery permits duplicates.

3 sections · 10 explained questions · About 10 minutesAll lessons →

Read each short explanation, work through the example, then answer a pop quiz. Every answer explains the reasoning. Incorrect answers unlock a fresh question on the same idea; the full lesson contains ten questions.

01Understand the basics

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A queue buffers work between producers and workers. It helps absorb bursts and temporary outages, but it does not create processing capacity. At-least-once delivery means a job can arrive again, so workers must tolerate repeats.

Section 1 question · 4 variations
Does at-least-once prevent duplicates?

02Balance throughput

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Compare the arrival rate with total sustainable processing capacity. Equal rates leave no spare capacity to drain a backlog or absorb variability. Check downstream limits before adding workers.

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50 jobs/s inputQueue40 jobs/s capacityBacklog grows 10/s
Section 2 question · 3 variations
At 50 arrivals/s and 60 completions/s, how fast can a backlog drain?

03Handle poison messages

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A message that always fails can consume retries indefinitely. Set a retry budget, capture the failure reason and move exhausted jobs to a dead-letter path for investigation and controlled replay.

Section 3 question · 3 variations
What should happen to a job that repeatedly fails validation?

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