Search

Lessons (29)

• ACID, Transactions & Locks

  Make multi-step changes correct with atomic transactions, isolation choices, constraints and short-lived locks. The bank-transfer …

• Transactions, Indexes & Concurrency

  … transactions protect invariants while indexes speed access and locks coordinate writers](/img/database-interviews/transactions.svg) Q8: What …

• Time, Consistency and Distributed Transactions

  Reason about clocks, ordering, split brain, locks, CRDTs and transactions without promising impossible global certainty. ![Distributed correctness: clocks …

• Delivery Guarantees: At-Most, At-Least & Exactly Once

  Can a message be lost? Delivered twice? Learn Kafka's three delivery semantics, idempotent producers, transactions for read …

• Database Indexing & Transactions

  … retry the transaction Transaction tips - Keep transactions short. Never wait for an HTTP call or user input inside …

• Data in Microservices: Sagas & the Outbox Pattern

  Each service owns its database, so how do you keep data consistent across services without a shared transaction …

• Storage Engines & Database Operations

  … Bound pool size, reserve capacity for critical traffic, set deadlines and investigate long transactions or slow queries. Backups …

• SQL vs NoSQL Databases

  … catches bad data, JOINs answer complex questions, ACID transactions keep money and inventory correct, and SQL is a …

• What Is Software Architecture?

  … Use PostgreSQL for the orders service Status Accepted (2026-09-28) Context Orders need multi-row transactions (order …

• Domain-Driven Design: Tactical Patterns

  … keeps boundaries clear 4. Use eventual consistency between aggregates One transaction changes one aggregate; others react to domain …

• Design an E-Commerce Checkout

  … Do not hold a database transaction open across payment. Handle unknown provider outcomes through reconciliation; expire reservations; isolate …

• Design a Reliable Notification System

  … Enforce consent/preferences before enqueueing, and isolate transactional from marketing traffic. Workers send and record provider ID plus …

• Real-Time, Pub/Sub, Webhooks and CDC

  … CDC Publish committed database changes Use an outbox/transaction log, not app guesses Delivery is usually at-least …

• SQL Interview Query Drills

  … cleanup, decide which row to keep in a transaction and add a unique constraint to prevent recurrence. Q25 …

• Views, Triggers & Stored Procedures

  … inputs. A trigger runs automatically from an event. Transaction-control and return-value capabilities vary by engine, so …

• Finding Service Boundaries with DDD

  … consistency boundaries An aggregate is a group of objects that must stay consistent together , changed in one transaction …

• SQL Language, Identifiers & Data Types

  … Many systems call COMMIT and ROLLBACK transaction-control statements. Q7: Identity, sequence and UUID An identity/auto-increment …

• Exactly-Once Payment Processing

  … A database transaction cannot include that network call. Unsafe Safe --- --- Check key → call provider → save Atomically create/get …

• DBMS Foundations, Keys & Normalization

  … Why DBMS instead of files? A DBMS centralizes data, supports concurrent access, transactions, constraints, authorization, backup/recovery and …

• Replication, Partitioning & Sharding

  … Cross-shard joins and transactions are expensive. Prefer colocating related data, asynchronous aggregates and explicit workflows. Do not …

• Monolith vs Microservices

  … function calls ❌ Slow, unreliable network calls Transactions ✅ One ACID database transaction ❌ Sagas, eventual consistency Testing end to end …

• CQRS & Event Sourcing

  … It stores every transaction : deposit $100, withdraw $30, deposit $50. The balance is simply the sum. You can …

• Kafka vs RabbitMQ & the Kafka Ecosystem

  … Capture (CDC) with Debezium reads the database's transaction log and turns every insert, update and delete into …

• Message Queues & RabbitMQ

  … properties.messageId)) return channel.ack(msg); await db.transaction(async (tx) = { await doTheWork(tx, job); await tx.processedMessages …

• Event-Driven Architecture

  … include versions/timestamps Lost events when saving + publishing Transactional outbox pattern Hard to debug "what happened?" Correlation IDs …

• Scaling, Load Balancing & Rate Limiting

  … Adding shards moves data. Consistent hashing minimises that Transactions across shards Hard; avoid them by design Rate limiting …

• Normalization & Denormalization

  … The event/transactional outbox or refresh job that updates the copy. 3. Acceptable freshness delay. 4. Rebuild and …

• Vertical Slice Architecture & the Modular Monolith

  … In-process (fast, reliable) Network (slow, can fail) Transactions ✅ Easy ✅ Easy within a module ❌ Sagas Operational complexity ✅ Low …

• Behavioral Patterns II: Chain, Template, Iterator, Mediator, Memento, Visitor

  … in Google Docs, Redux DevTools time travel, database transactions (rollback). 💡 Memento vs Command for undo: Memento stores snapshots …