How do you safely implement Database Transactions and isolation levels in Node.js?

Short answer

Reserve a specific client from the pool, run BEGIN and the operations, then COMMIT on success or ROLLBACK in a catch block.

Explanation

A transaction guarantees Atomicity in ACID: either every change succeeds or all of them are rolled back. It is essential to use the same Dedicated Client for every operation in a transaction, because pool.query() distributes operations across different connections and completely breaks the transaction.

Code example

const client = await pool.connect();
try {
  await client.query("BEGIN");
  await client.query("UPDATE accounts SET balance = balance - 100 WHERE id = $1", [from]);
  await client.query("UPDATE accounts SET balance = balance + 100 WHERE id = $1", [to]);
  await client.query("COMMIT");
} catch (e) {
  await client.query("ROLLBACK");
  throw e;
} finally {
  client.release();   // return the dedicated connection to the pool
}

Common mistakes

• Running BEGIN and COMMIT directly through pool.query instead of a reserved, dedicated client.

Follow-up questions

• How do database Connection Pools work, and what are the risks of exhausting them in Node.js?

Sources

• node-postgres docs — Transactions
• PostgreSQL docs — Transaction Isolation