DataLoader batching and caching in GraphQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main purpose of DataLoader in GraphQL?

DataLoader helps to batch and cache database or API requests to reduce the number of calls and improve performance.

intermediate

How does DataLoader batch requests?

DataLoader collects multiple requests for data during a single tick of the event loop and sends them as one combined request to the database or API.

beginner

What is caching in DataLoader and why is it useful?

Caching means storing the result of a request so if the same data is requested again, DataLoader returns the cached result instead of making a new request. This saves time and resources.

intermediate

Can DataLoader cache be disabled? If yes, why would you do that?

Yes, DataLoader cache can be disabled if you want fresh data every time or if caching causes stale data issues in your application.

intermediate

What happens if you create a new DataLoader instance for every request?

Creating a new DataLoader per request ensures caching and batching are isolated per request, preventing data leaks between users and ensuring fresh cache per request.

What does DataLoader primarily help to reduce in GraphQL applications?

A Number of database or API calls

B Number of GraphQL queries

C Size of the database

D Number of frontend components

DataLoader batches multiple requests into one, reducing the number of database or API calls.

When does DataLoader send the batched requests to the database?

A Only when cache is empty

B Immediately after each request

C After 1 minute delay

D At the end of the event loop tick

DataLoader waits until the current event loop tick finishes to batch all requests together.

What is a benefit of caching in DataLoader?

A It avoids repeated fetching of the same data

B It slows down the application

C It deletes old data automatically

D It increases the number of requests

Caching avoids fetching the same data multiple times, improving performance.

Why might you disable caching in DataLoader?

A To reduce memory usage

B To always get fresh data

C To increase batch size

D To speed up caching

Disabling cache ensures you get fresh data every time, useful if data changes frequently.

What is a recommended practice for using DataLoader in a server handling multiple users?

A Use a single global DataLoader instance

B Disable batching

C Create a new DataLoader instance per request

D Cache data forever

Creating a new DataLoader per request prevents data leaks and ensures isolated caching.

Explain how DataLoader batching works and why it improves performance.

Think about how requests are grouped before sending.

Describe the role of caching in DataLoader and when you might want to disable it.

Consider the trade-off between speed and data freshness.