Improve node app responsiveness using partitioning
Source: Dev.to
Problem Statement
We have a single GET endpoint that fetches documents from a database, transforms them, and returns the result. For some clients we need to fetch a large number of documents, which blocks Node’s event‑loop thread. When the event loop is blocked:
- The app becomes unresponsive to new requests.
- The liveness probe fails and Kubernetes restarts the pod.
- Small, fast requests experience unpredictable delays.
Restarts became very frequent, and we cannot simply add pagination and deprecate this legacy endpoint. We need a short‑term solution that requires minimal code changes to prevent restarts and improve application responsiveness.
Solution
Node.js provides a technique called partitioning. The idea is to break large synchronous processing into smaller tasks and yield to the event loop between each task, allowing other requests to be handled.
// Return a Promise that resolves on the next tick, letting the event loop process other work.
function yieldToEventLoop(): Promise {
return new Promise((resolve) => setImmediate(resolve));
}
for (let i = 0; i < docs.length; i += smallBatchSize) {
const batch = docs.slice(i, i + smallBatchSize);
// Process the current batch
output.push(...processBatch(batch));
// Yield to the event loop before processing the next batch
await yieldToEventLoop();
}By inserting await yieldToEventLoop() after each batch, the event loop can serve other requests, preventing a single heavy request from starving the entire process.
Key Takeaway
- This approach does not make processing faster or reduce CPU usage.
- It improves the responsiveness of the application.
- Chunking work and yielding to the event loop keeps the process alive and provides temporary relief.
If your server performs heavy computations, consider whether Node.js is the right fit. Node excels at I/O‑bound workloads, but expensive CPU‑bound work may be better handled elsewhere. See the Node.js documentation on partitioning for more details.