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How do you fix “cursor not found” errors during data retrieval?

The error “cursor not found” in MongoDB typically occurs when a query or cursor is inactive, expired, or invalidated before data retrieval is complete.

How do you fix “cursor not found” errors during data retrieval?

🔍 What Does “Cursor Not Found” Mean?

A cursor in MongoDB is a pointer to the result set of a query. The error:

cursor not found

means:

  • The cursor was killed or timed out on the server before all results were read.

  • A subsequent getMore operation failed because the cursor no longer exists.

🧯 Common Causes and Fixes

✅ 1. Cursor Timed Out on Long Operations

By default, server-side cursors expire after 10 minutes of inactivity.

✅ Fix:

Use a no-timeout cursor if the operation takes a long time:

Shell:

db.collection.find().noCursorTimeout()

Driver (Node.js example):

collection.find({}, { noCursorTimeout: true })

🧠 Reminder: Close the cursor manually when done to avoid memory leaks:


cursor.close();

✅ 2. Network Drop or Client Disconnect

If the client disconnects (e.g., due to a crash or timeout), the server may clean up the cursor.

✅ Fix:

✅ 3. Using batchSize Too Large

A large batchSize can delay responses or overwhelm memory, leading to timeouts.

✅ Fix:

Set a reasonable batchSize:

db.collection.find().batchSize(1000)

✅ 4. Using awaitData or Tailable Cursors Incorrectly

Tailable cursors (on capped collections) can return this error if not managed correctly.

✅ Fix:

  • Make sure you're using them only on capped collections.

  • Ensure your application logic handles null or no-data responses gracefully.

✅ 5. Cursor Already Exhausted

If you try to fetch from a cursor that's already been fully iterated, MongoDB will return this error.

✅ Fix:

Don’t reuse a cursor after it's closed or done:

while (await cursor.hasNext()) {
  const doc = await cursor.next();
}

✅ Best Practices

TipWhy It Helps
Use .noCursorTimeout() carefullyPrevents auto-timeout but must be closed manually
Set batchSize appropriatelyImproves performance and avoids overload
Use pagination (skip/limit) if possibleReduces cursor usage for large sets
Monitor server logsCheck for cursor timeouts and resource limits

🧠 Summary

  • Use .noCursorTimeout() if query takes long

  • Set appropriate batchSize

  • Retry safely on client/network error

  • Don’t reuse exhausted cursors

  • Use logging and monitoring to diagnose root causes

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