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How do database transactions work in Node.js and how do you avoid connection leaks?

Q: How do database transactions work in Node.js and how do you avoid connection leaks?

**TL;DR.** A transaction runs BEGIN → your queries → COMMIT (or ROLLBACK on error) on a **single** connection checked out from the pool, giving **all-or-nothing** atomicity. The classic leak is forgetting to **release** that connection on an error path — so always release in a finally (or use the driver's managed-transaction helper). BEGIN queries <path class='d-edge-dashed' d='M214 87 H

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Understand the problem

BEGIN/COMMIT/ROLLBACK on a pooled connection and try/finally release.

nodejsdatabasetransactionspooling

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Read the code

Transaction with guaranteed release

async function transfer(from, to, amount) {
  const client = await pool.connect();
  try {
    await client.query('BEGIN');
    await client.query('UPDATE acct SET bal = bal - $1 WHERE id=$2', [amount, from]);
    await client.query('UPDATE acct SET bal = bal + $1 WHERE id=$2', [amount, to]);
    await client.query('COMMIT');
  } catch (e) {
    await client.query('ROLLBACK');
    throw e;
  } finally {
    client.release();          // ALWAYS — even on error
  }
}

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