Question 1

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

Accepted Answer

A pool manages a set of pre-opened connections and shares them among requests; exhausting it queues requests and increases response times and timeouts.

Question 2

How does Prisma ORM work in Node.js, and what role does its Query Engine / Query Compiler play?

Accepted Answer

Prisma generates a custom TypeScript client from schema.prisma and translates calls into SQL. It used to run through a Rust binary engine; recent versions (available since 6.16 and the default in Prisma 7) use a TypeScript Query Compiler with driver adapters and no Rust engine.

Question 3

Compare Drizzle ORM and TypeORM in terms of architecture and performance in Node.js.

Accepted Answer

Drizzle is a lightweight, zero-overhead SQL-like query builder without binary engines, while TypeORM is a traditional ORM using the Data Mapper/Active Record patterns and relying on reflection and decorators.

Question 4

How does Mongoose manage its MongoDB connection, and what is the role of command Buffering?

Accepted Answer

Mongoose provides an advanced ODM layer; Command Buffering lets model queries be issued before the initial connection is ready and queues them until the connection succeeds.

Question 5

How do parameterized queries protect Node.js applications from SQL Injection?

Accepted Answer

Parameterized queries separate SQL code from data through placeholders ($1, ?); the database receives parameter values as literals that cannot be interpreted as code.

Question 6

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

Accepted Answer

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

Question 7

What is the N+1 problem in database queries, and how does DataLoader solve it in Node.js?

Accepted Answer

It occurs when one main query is followed by N queries, one per record, to fetch related data; DataLoader batches and caches requests into a unified query.

Question 8

How do you design query routing between a Primary database and Read Replicas?

Accepted Answer

Create two separate connection pools: one for the Primary for writes and transactions, and one for Replicas for reads with load balancing.

Question 9

How do you perform Database Migrations without service downtime (Zero-Downtime)?

Accepted Answer

Follow the Expand and Contract pattern so the database schema supports both the old and new application code during deployment.

Question 10

How do you implement Distributed Locks with Redis across multiple Node.js servers?

Accepted Answer

Use SET with NX and PX options to store a random token with a timeout, and release the lock with a Lua script that verifies the token.