AWS lambda async db (Firestore) query, why returns Promise{<pending>}

Question

var db = admin.firestore();

exports.handler = async (event) => {
    let res = await db.collection(`apps/${event.app_id}/whitelist`).doc(event.ip).set({
        ip: event.ip
    }).then(() => {
        return {
            statusCode: 200,
            body: {
                message: 'success'
            }
        };
    }).catch(() => {
        return {
            statusCode: 400,
            body: {
                message: 'failed'
            }
        };
    });
    return res;
};

This code will result in timeout on Lambda, and console.log(exports.handler(event)) will print Promise{<pending>} .
My questions are
1. What does Lambda expect for this async function; what should it return?
2. Promise{<pending>} means unresolved promise, but in the code, res will finally be a value/object, then why it still says unresolved.
3. What are some nice references we can lookup?

Thanks.

Answer 1

pic

Guys... just allocate more memory for your lambda.

I tried the above code on local and it finished in 0.05s, and it reached 3s time limit on lambda, so I think it should be my promise's error. But in fact, the promise is correct, and it should be a pending promise since the outside function has never been resolved. It is slow since it has too less memory (128mb). Give it more memory and the error goes away.