hard20 pts · first answer countsdatabasesperformancesystem-design

Pool exhausted during payments

Checkout opens a transaction, inserts the order, calls the payment provider over HTTP (2 to 5 seconds), then commits. With a pool of 20 connections, checkout times out at peak. What is the best redesign?

A.Raise the pool size to 500 connections and set the database max_connections high enough to cover every single app instanceB.Use READ UNCOMMITTED so the transaction finishes fasterC.Wait forever for a free connection instead of timing outD.Commit the order as pending first, call the provider with an idempotency key, then update it in a new short transaction

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