Refetching and polling in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the result of polling with a 5-second interval?

Consider a GraphQL query that fetches the current server time. The client sets up polling with a 5-second interval. What will the client receive?

GraphQL

query GetServerTime {
  serverTime
}

// Client polls every 5 seconds

A The client receives server time updates randomly, not every 5 seconds.

B The client receives the same server time repeatedly without updates.

C The client receives server time only once at the start.

D The client receives updated server time every 5 seconds.

💡 Hint

Polling means the client asks the server repeatedly at fixed intervals.

Polling with a 5-second interval means the client sends the query every 5 seconds and receives the latest server time each time.

🧠 Conceptual

intermediate

Why use refetching instead of polling in GraphQL?

Which reason best explains why a developer might choose to use refetching over polling?

A Refetching allows manual control to update data only when needed, saving resources.

B Refetching sends queries continuously at fixed intervals.

C Refetching caches data permanently and never updates it.

D Refetching automatically updates data without any user action.

💡 Hint

Think about when you want to update data only sometimes, not all the time.

Refetching is a manual or event-triggered way to update data, which helps avoid unnecessary network requests compared to polling.

📝 Syntax

advanced

Which polling setup syntax is correct in Apollo Client?

Choose the correct way to set up polling every 10 seconds in Apollo Client.

GraphQL

const { data, loading, error } = useQuery(GET_DATA, {
  // polling setup here
});

A pollingInterval: 10000

B pollInterval = 10000

C pollInterval: 10000

D pollInterval: '10000'

💡 Hint

Check the exact property name and value type for polling interval.

The correct property is pollInterval with a number value in milliseconds.

🔧 Debug

advanced

Why does refetching not update data immediately?

A developer calls refetch() on a query, but the UI does not update with new data. What is the most likely cause?

A The <code>refetch()</code> method is asynchronous and must be awaited.

B The query is missing a <code>fetchPolicy</code> that allows network requests.

C The server does not support refetching queries.

D The query is cached and cannot be updated.

💡 Hint

Think about how Apollo Client decides where to get data from.

If the fetch policy is set to only use cache, refetching won't trigger a network request to get fresh data.

❓ optimization

expert

How to optimize polling to reduce server load?

You have a GraphQL query polling every 2 seconds, but the server load is too high. Which approach best reduces load while keeping data fresh?

A Increase polling interval to 30 seconds and use refetch on user actions.

B Keep polling every 2 seconds but disable caching completely.

C Use polling every 2 seconds but add a delay in the server response.

D Remove polling and rely only on initial query load.

💡 Hint

Think about balancing update frequency and server requests.

Increasing the polling interval reduces requests, and refetching on user actions keeps data fresh when needed.