Introduction

Every millisecond matters in API performance. When you're building APIs that serve thousands of users, speed becomes critical. Let's look at how to make APIs faster, starting from the database and moving up to the user's device.

Database Optimization

Database optimization comes first because that's where most slowdowns happen. Think of your database like a library. Without an index, you'd need to check every book to find what you want.

Database indexes work the same way, they help find data quickly. But don't overdo it. Each index makes writes slower, just like how adding more library catalogs would make shelving books take longer.

Connection pooling is another database trick. Instead of creating new database connections for each request, we keep a pool of ready-to-use connections. The reason this helps is because if the server doesn't have a connection to the database, it needs to open one (several steps under the hood). This operation usually takes 10-100ms depending on the current load.

Application Level Optimization

Moving up to the application level, caching is your next powerful tool. Redis is great for this. When data doesn't change often, store it in Redis instead of hitting the database. It's like keeping frequently checked-out books at the front desk instead of fetching them from the shelves every time.

The way you handle the data matters too. Always send only what's needed. If someone asks for a user's name, don't pull their entire profile. In GraphQL for example, watch out for the N+1 query problem, when you fetch a list of items and then make separate queries for each item's details. Use DataLoader to batch these requests together.

Now let's talk about the actual response. Compression can make your responses smaller and faster to send. In Node.js for example, it's as simple as adding compression middleware:

app.use(
  compression({
    level: 6, // Balance between speed and compression
    threshold: 1024, // Only compress responses bigger than 1KB
  })
);

Monitoring

But how do you know if these changes actually help? This is where monitoring comes in. Distributed tracing lets you follow a request's journey through your system. It shows you exactly where time is spent, like a GPS tracking a delivery truck's route. Tools like OpenTelemetry can help with this:

const span = tracer.startSpan("database-query");
try {
  const result = await db.query("SELECT * FROM users");
  span.end();
  return result;
} catch (error) {
  span.recordException(error);
  span.end();
  throw error;
}

Infrastructure Optimization

CDNs can serve content from locations closer to your users.

Load balancers can distribute traffic evenly across servers.

And don't forget about geographic distribution, having servers in different regions can significantly reduce response times for users worldwide.