Updating documents in Express - Performance & Optimization

Performance: Updating documents

MEDIUM IMPACT

This affects server response time and client perceived latency when updating data that triggers UI changes.

Updating a document in a database and sending the updated data to the client

Express

app.put('/item/:id', async (req, res) => {
  const id = req.params.id;
  const update = req.body;
  const result = await db.collection('items').findOneAndUpdate(
    {_id: new ObjectId(id)},
    {$set: update},
    {returnDocument: 'after'}
  );
  res.send(result.value);
});

Single atomic database call reduces latency and server load.

📈 Performance GainSaves 50-100ms per request by avoiding redundant DB fetch

Updating a document in a database and sending the updated data to the client

Express

app.put('/item/:id', async (req, res) => {
  const id = req.params.id;
  const update = req.body;
  const doc = await db.collection('items').findOne({_id: new ObjectId(id)});
  Object.assign(doc, update);
  await db.collection('items').updateOne({_id: new ObjectId(id)}, {$set: doc});
  res.send(doc);
});

Fetching the document first then updating causes two database operations and delays response.

📉 Performance CostBlocks response for extra 50-100ms due to double DB calls

Performance Comparison

Pattern	DB Calls	Server Delay	Network Payload	Verdict
Fetch then update	2 calls (findOne + updateOne)	High (extra 50-100ms)	Larger (full doc sent back)	[X] Bad
Atomic findOneAndUpdate	1 call	Low (minimal delay)	Smaller (only updated doc)	[OK] Good

Rendering Pipeline

Updating documents on the server affects the time until the client receives updated data and can re-render UI. The server processing delays INP (input responsiveness) as the client waits for confirmation.

→Server Processing

→Network Transfer

→Client Rendering

⚠️ BottleneckServer Processing due to multiple DB calls or inefficient updates

Core Web Vital Affected

INP

This affects server response time and client perceived latency when updating data that triggers UI changes.

Optimization Tips

1Use atomic update operations to reduce database calls.

2Send minimal updated data to the client to reduce network payload.

3Batch updates when possible to avoid multiple server round-trips.

Performance Quiz - 3 Questions

Which update pattern reduces server processing time when updating a document?

A Sending the entire document back to the client after update

B Using a single atomic update operation like findOneAndUpdate

C Fetching the document first, then updating it separately

D Updating the document multiple times in a loop

DevTools: Network

How to check: Open DevTools Network tab, perform the update request, and observe the request duration and response size.

What to look for: Look for longer request times and larger response payloads indicating inefficient updates.