Size the pool to the lowest total cost.

Too small and requests queue (wait cost); too large and you pay for idle connections. The minimum sits just above the offered load (~8 in-flight).

Practice — no rating pressure. Get as close to the optimum as you can; each play teaches the pattern.

Total cost

1486

10 connections

cost by pool size (shorter is cheaper)

Pool size

The Connection Pool — practice the decision, scored against the optimum

What does the The Connection Pool puzzle teach?

Pool size is a U-curve — too small queues requests, too large wastes idle connections.

Why do interviews ask about this?

Connection-pool sizing is the classic “why is the DB slow” interview: too few starves, too many thrashes — find the knee.

How is it scored?

The engine computes the provably-optimal answer for the exact instance you played (dynamic programming, shortest-path, or exhaustive search — never a heuristic) and scores your attempt as a percentage of it. No login needed to see your score.

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Practice0:00

The Connection Pool · D1

Size the pool to the lowest total cost.

Too small and requests queue (wait cost); too large and you pay for idle connections. The minimum sits just above the offered load (~8 in-flight).

Practice — no rating pressure. Get as close to the optimum as you can; each play teaches the pattern.

Total cost

1486

10 connections

cost by pool size (shorter is cheaper)

Pool size