How to Efficiently Rename a Field Across 1 Million MongoDB Documents?

I’m facing a scenario where I need to rename a field across a large MongoDB collection consisting of approximately 1 million documents. I’m looking for the most efficient way to accomplish this task to minimize downtime and ensure optimal performance.

Here’s the current approach I’m using with Mongoose:

async function renameField() {
    await mongoose.connect(MONGODB_URL);
    const userModel = mongoose.connection.db.collection("users");
    const result = await userModel.updateMany({}, { $rename: { new_email: "email" } });
}

renameField().catch(console.error);

Hi Albert! Thank you for your question!

The code snippet you shared looks accurate, assuming that new_email is the previous field name and email is the desired new field name.

Here are some general suggestions:

  1. updateMany doesn’t update all documents in a single atomic operation. This is fine because you’re updating 1M documents and locking them wouldn’t be desirable.

  2. Back up your collection before running the migration.

  3. You must have an index on the updated field! You don’t want to scan 1M un-indexed documents. Create an index and then, after the migration runs, remove it. You can also hint to the query engine that it must use the index when running the update:

await collection.createIndex({ oldFieldName: 1 });

const result = await collection.updateMany(
    {}, 
    {
        $rename: { oldFieldName: "newFieldName" }
    },
    {
        hint: { oldFieldName: 1 }
    }
);

// Drop the old field index
await collection.dropIndex("oldFieldName_1");

// Create an index on the new field if you need it
await collection.createIndex({ newFieldName: 1 });

  1. Verify that the operation ran successfully and there are no docs with the old field name left:
await collection.findOne({oldFieldName: {$exists: true}}); // this should not return any documents