Connection pooling in HLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why use connection pooling in a web application?

Imagine a busy coffee shop where each customer must wait for a new cup to be made before ordering. How does connection pooling help improve efficiency in a similar way for web applications?

A It creates a new connection for every request to ensure freshness.

B It reuses existing connections to reduce the overhead of creating new ones.

C It closes all connections immediately after use to save resources.

D It limits the number of users who can access the application at once.

💡 Hint

Think about how reusing resources can save time and effort.

Connection pooling keeps a set of open connections ready to use, so the application does not need to create a new connection for every request. This saves time and system resources.

❓ Architecture

intermediate

Which component is responsible for managing connection pools in a typical system design?

In a layered system design, where should the connection pool be placed to best serve multiple application requests?

A Within the application server to manage database connections for requests.

B In the network layer to manage all traffic connections.

C On the client side to manage connections to the application server.

D Directly inside the database server to manage client connections.

💡 Hint

Think about where the application talks to the database.

The connection pool is usually managed by the application server because it handles multiple requests that need database access. This allows efficient reuse of database connections.

❓ scaling

advanced

How does connection pooling help scale a high-traffic web application?

Consider a web app receiving thousands of requests per second. How does connection pooling support scaling under this load?

A By creating unlimited new connections for each request to avoid waiting.

B By closing connections immediately after each request to free resources.

C By limiting the number of concurrent connections and reusing them efficiently.

D By distributing requests evenly across multiple databases without pooling.

💡 Hint

Think about resource limits and reuse under heavy load.

Connection pooling limits the number of open connections to a manageable number and reuses them, preventing resource exhaustion and improving response times under heavy traffic.

❓ tradeoff

advanced

What is a tradeoff when using a very large connection pool size?

Increasing the connection pool size seems beneficial. What is a downside of having too many connections open at once?

A It increases resource consumption and can overload the database server.

B It simplifies connection management by avoiding reuse.

C It guarantees no request will ever wait for a connection.

D It reduces latency by always having connections ready.

💡 Hint

Think about system limits and resource usage.

While a large pool reduces waiting time, it consumes more memory and CPU on the database server, which can degrade overall system performance.

❓ estimation

expert

Estimate the maximum number of concurrent requests supported by a connection pool of size 50 if each request holds a connection for 100ms and requests arrive evenly at 10 per second.

Given a connection pool size of 50, each request uses a connection for 100 milliseconds, and requests arrive evenly at 10 per second, what is the maximum number of concurrent requests the system can handle without waiting?

A 100 concurrent requests

B 10 concurrent requests

C 20 concurrent requests

D 50 concurrent requests

💡 Hint

Calculate how many requests can use connections simultaneously based on pool size and request duration.

Each connection can serve 10 requests per second (1000ms / 100ms). With 50 connections, the system can handle 50 concurrent requests at once without waiting.