Connection pooling in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the main benefit of connection pooling in databases?

Connection pooling helps manage database connections efficiently. What is the primary advantage of using connection pooling?

A It increases the size of the database storage automatically.

B It encrypts all data sent between the client and the database.

C It automatically backs up the database at regular intervals.

D It reduces the time needed to establish a new connection by reusing existing ones.

💡 Hint

Think about what happens when you open and close connections repeatedly.

Connection pooling keeps a set of open connections ready to use, so the system doesn't waste time opening new connections each time.

❓ query_result

intermediate

How many connections are active after these GraphQL queries?

Assume a GraphQL server uses a connection pool with a maximum of 5 connections. Three queries run simultaneously, each requiring a connection. How many connections are active during this time?

A 5

B 3

C 1

D 0

💡 Hint

Each query needs one connection from the pool.

Since three queries run at the same time, three connections are checked out from the pool and active.

📝 Syntax

advanced

Identify the correct GraphQL connection pool configuration snippet

Which of the following snippets correctly sets a connection pool with a maximum of 10 connections in a GraphQL server using a typical Node.js setup?

A const pool = new Pool(max = 10);

B const pool = new Pool({ max_conn: 10 });

C const pool = new Pool({ max: 10 });

D const pool = new Pool({ maxConnections: 10 });

💡 Hint

Look for the standard property name for max connections in pool config.

The correct property to set max connections is 'max' inside the config object.

❓ optimization

advanced

Optimizing connection pool size for a GraphQL API

If a GraphQL API experiences slow responses due to waiting for database connections, which adjustment to the connection pool is most likely to improve performance?

A Increase the maximum number of connections in the pool.

B Decrease the maximum number of connections in the pool.

C Disable connection pooling to open new connections each time.

D Set the pool size to zero.

💡 Hint

More connections can handle more simultaneous requests.

Increasing the pool size allows more queries to get connections without waiting, improving response times.

🔧 Debug

expert

Why does this GraphQL server crash with 'too many clients' error?

A GraphQL server uses a connection pool with max 5 connections. The server crashes with 'too many clients' error. Which is the most likely cause?

GraphQL

const pool = new Pool({ max: 5 });

async function resolver() {
  const client = await pool.connect();
  // forgot to release client
  // client.release();
  return await client.query('SELECT * FROM users');
}

A Clients are not released back to the pool, exhausting available connections.

B The query syntax is incorrect causing the crash.

C The max pool size is too large causing overload.

D The pool is not initialized properly.

💡 Hint

Check if connections are returned to the pool after use.

Not releasing clients causes the pool to run out of available connections, leading to errors.