Simple concurrency limiter for batch operations

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                  export function limit(concurrency: number) {
  let active = 0;
  const queue: Array<() => void> = [];

  const next = () => {
    active -= 1;
    queue.shift()?.();
  };

  return async function <T>(fn: () => Promise<T>): Promise<T> {
    if (active >= concurrency) {
      await new Promise<void>((resolve) => queue.push(resolve));
    }
    active += 1;
    try {
      return await fn();
    } finally {
      next();
    }
  };
}

Unbounded Promise.all is a great way to overload your DB (or a third-party API). I use a small concurrency limiter so I can process batches efficiently while keeping backpressure. This is especially useful for migrations, backfills, and webhook replays where you might touch thousands of records. I like making concurrency configurable via env so I can tune it per environment without code changes. The main idea is being intentional about resource usage: your service has a finite DB pool and a finite CPU budget. A limiter keeps throughput high without turning background tasks into accidental stress tests.

Mateo Rodriguez

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Simple concurrency limiter for batch operations

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