How to Fix Cursor Not Found Error in MongoDB

The cursor not found error in MongoDB happens when the cursor is closed or timed out before fetching all results. To fix it, ensure you fully iterate the cursor promptly or increase the cursor timeout using noCursorTimeout option when creating the cursor.

Why This Happens

This error occurs because MongoDB closes cursors that are idle for too long or when the client tries to use a cursor that has already been closed. For example, if you fetch some results but then wait too long before continuing, the server may close the cursor, causing the error.

javascript

const cursor = db.collection('users').find({});

// Simulate delay before fetching next batch
setTimeout(async () => {
  const doc = await cursor.next();
  console.log(doc);
}, 360000); // 6 minutes delay

Output

MongoError: cursor not found, cursor id: 1234567890

The Fix

To fix this, either consume the cursor quickly without long delays or create the cursor with noCursorTimeout: true to prevent the server from closing it automatically. Use this option carefully to avoid resource leaks.

javascript

const cursor = db.collection('users').find({}, { noCursorTimeout: true });

// Now you can safely delay or process results slowly
setTimeout(async () => {
  const doc = await cursor.next();
  console.log(doc);
  await cursor.close(); // Always close cursor when done
}, 360000); // 6 minutes delay

Output

{ _id: ObjectId('...'), name: 'Alice', age: 30 }

Prevention

To avoid this error in the future, always process cursors promptly and close them when done. Use noCursorTimeout only when necessary and remember to close cursors manually. Also, consider using toArray() for small result sets to fetch all data at once.

Implement proper error handling to catch cursor errors and retry queries if needed.

Related Errors

Other similar errors include:

• CursorNotFound: Happens when the cursor ID is invalid or expired.
• OperationTimedOut: When a query takes too long to execute.
• NetworkTimeout: When the connection to MongoDB is lost during cursor iteration.

Quick fixes usually involve retrying the query, increasing timeouts, or ensuring cursors are handled correctly.

Key Takeaways

The 'cursor not found' error happens when MongoDB closes an idle cursor before you finish using it.

Use the 'noCursorTimeout' option to keep cursors alive longer but always close them manually.

Process cursor results promptly to avoid timeouts and resource issues.

For small datasets, use 'toArray()' to fetch all results at once and avoid cursor issues.

Implement error handling to catch and recover from cursor-related errors.