What causes database deadlocks, and how do you prevent them in a busy OLTP system?
⚡ Short Answer
Two transactions acquire the same rows/locks in opposite order and wait on each other; the DB detects the cycle and kills one (deadlock victim). Prevent with a consistent lock/update order, short transactions, the right indexes (to lock fewer rows), and retry logic on the victim.
☕Coffee Chat Question
Concept Made Simple
“What causes database deadlocks, and how do you prevent them in a busy OLTP system?”
🧠Mind Map Answer
Remember It Faster
🔥What If?
Think Beyond the Expected
Why can a MISSING index actually cause more deadlocks?
Without a good index, a query scans and locks far more rows (or escalates to range/table locks), widening the window for lock conflicts. Adding the right index narrows locking to the exact rows, reducing both contention and deadlocks.
😂Real World
OLTP deadlocks (order/inventory/ledger) are routine under load; the durable fixes are consistent update ordering, keeping transactions short, indexing to lock fewer rows, and idempotent retry on the deadlock victim.
🎯Interviewer's Expectation
Keywords they're listening for:
⚠️Common Mistakes
- ✗Updating rows in inconsistent order across code paths
- ✗Long transactions holding locks across external calls
- ✗No retry on the deadlock victim
✅Best Practices
- ✓Acquire/update rows in a consistent order
- ✓Keep transactions short; index to lock fewer rows
- ✓Implement idempotent retry on deadlock errors
🔁Follow-up Questions
- 1How do you read a deadlock graph / log?
- 2Why do shorter transactions reduce deadlocks?
- 3How does lock escalation contribute?
🧩Related Technologies
Continue Learning with AI
Take this question deeper with your favourite AI assistant. Pick a depth, copy the prompt, or open it directly — AI is your learning companion, not a shortcut.
Plain-language foundations
I'm preparing for a software engineering interview and want to understand this from scratch, as a beginner. Topic: Transactions (SQL) Interview question: "What causes database deadlocks, and how do you prevent them in a busy OLTP system?" Please: 1. Explain the core idea in simple, plain language, using an everyday analogy. 2. Define any technical terms you use. 3. Walk through one small, concrete example. 4. Finish with a single sentence I can easily remember. Keep the tone friendly and assume I'm new to this topic.
Was this answer helpful?
⭐ Featured Products
Support our platform by exploring our recommended products.
As an Amazon affiliate, purchases through these links may earn us a small commission — at no extra cost to you. It helps keep Full Stack Interview Guru free.