Promise.all() 比对每个 promise 使用 await 慢吗？

Question

I'm doing some testing for performance and was looking at Promise.all() in node.js. However, after testing this it's actually slower than using await for the 3 promises I want to resolve. I'm simply returning some data back from a mongodb database.

Am I doing something wrong here or is this just due to the way the event loop is working?

Promise.all(): 234.820ms

  // Init db connection
  const db = client.db('docker-client1');
  const productsCollection = db.collection('ICProductData');
  const rulesCollection = db.collection('SPRuleData');
  const customersCollection = db.collection('ARCustomerData');
  // Main function

  const CustomerCode = 'FINE';
  const ProductCode = 'BEDCABINET';

  let customers = customersCollection
    .find({ _id: CustomerCode })
    .project({ PriceCode: 1, BillToAccountCode: 1 })
    .toArray();

  let products = productsCollection
    .find({ _id: ProductCode })
    .project({ 'Price.PriceCode': 1, 'Price.SellingPrice': 1 })
    .toArray();

  let rules = rulesCollection
    .find({
      $and: [
        {
          $or: [
            {
              $and: [
                { What1Code: ProductCode, What1Type: 'Product' },
                { Who1Code: CustomerCode, Who1Type: 'Customer' }
              ]
            }
          ]
        }
      ]
    })
    .toArray();

  const results = await Promise.all([customers, products, rules]);
  console.timeEnd();

Simply using await: 127.239ms

  // Init db connection
  const db = client.db('docker-client1');
  const productsCollection = db.collection('ICProductData');
  const rulesCollection = db.collection('SPRuleData');
  const customersCollection = db.collection('ARCustomerData');
  // Main function

  const CustomerCode = 'FINE';
  const ProductCode = 'BEDCABINET';

  const custReq = await customersCollection
    .find({ _id: CustomerCode })
    .project({ PriceCode: 1, BillToAccountCode: 1 })
    .toArray();
  const prodReq = await productsCollection
    .find({ _id: ProductCode })
    .project({ 'Price.PriceCode': 1, 'Price.SellingPrice': 1 })
    .toArray();

  let rulesReq = await rulesCollection
    .find({
      $and: [
        {
          $or: [
            {
              $and: [
                { What1Code: ProductCode, What1Type: 'Product' },
                { Who1Code: CustomerCode, Who1Type: 'Customer' }
              ]
            }
          ]
        }
      ]
    })
    .toArray();

  console.timeEnd();

Answer 1

The method toArray() does not return a Promise in Old versions of Mongo. This could be the explanation about timings. You could put a console.log with timing after each toArray() they should run in the same millisecond (same tick). If this is not the case, it could be an indication that toArray() is waiting for the response... so you are running sequentially. You could try to resolve this with: let myProm = collection.find(filter).exec()