Transactions

What a Transaction Is

A transaction groups multiple queries into a single atomic unit: either all succeed or all fail. This prevents partial updates and data corruption.

When You Need Transactions

Use transactions when multiple tables/rows must stay consistent: payment records, inventory updates, logging + main write, or moving money between accounts.

Basic Transaction Example

Wrap related queries in beginTransaction() / commit(). On error, rollback.

<?php
try {
  $pdo->beginTransaction();

  $stmt1 = $pdo->prepare("INSERT INTO orders (user_id, total) VALUES (?, ?)");
  $stmt1->execute([1, 144.00]);

  $orderId = (int)$pdo->lastInsertId();

  $stmt2 = $pdo->prepare("INSERT INTO order_items (order_id, sku, qty) VALUES (?, ?, ?)");
  $stmt2->execute([$orderId, "SKU-123", 2]);

  $pdo->commit();
  echo "OK";
} catch (Throwable $e) {
  if ($pdo->inTransaction()) {
    $pdo->rollBack();
  }
  // log $e in production
  echo "Failed";
}

Transaction Gotchas

Do not keep transactions open too long (slow requests, external API calls). Keep the transaction scope minimal: validate first, then open transaction, run queries, commit.

Production Tip

Transactions are a correctness tool. Use them whenever partial writes would break invariants. Combine with proper indexes and short transaction windows to avoid lock contention.