MongoDB-aggregation-benchmark.js

const N = 1000;

db.items.remove({});
db.users.remove({});

db.items.createIndex({ features: 1, owner: 1 });
db.users.createIndex({ items: 1 });
db.users.createIndex({ partner: 1 });

for (let i = 0; i < N; i++) {
  const user = i; // ObjectId();
  const item = i; // ObjectId();
  db.items.insert({ _id: item, size: Math.random(), owner: user });
  db.users.insert({ _id: user, items: [item], partner: N - user - 1 });
}

print("\nMatch + 2 lookups");

let before = new Date();

let r = db.items
  .aggregate([
    {
      $match: { size: { $lt: 0.5 } }
    },
    {
      $lookup: {
        as: "owner",
        from: "users",
        let: { id: "$_id" },
        pipeline: [
          { $match: { $expr: { $in: ["$$id", "$items"] } } },
          {
            $lookup: {
              as: "partner",
              from: "users",
              let: { id: "$_id" },
              pipeline: [{ $match: { $expr: { $eq: ["$$id", "$partner"] } } }]
            }
          },
          { $project: { partner: { $arrayElemAt: ["$partner", 0] } } }
        ]
      }
    },
    { $project: { size: 1, owner: { $arrayElemAt: ["$owner", 0] } } }
  ])
  .toArray();

// printjson(r[0]);
// printjson(r.length);

print("Aggregation 1:", new Date() - before, "ms");

before = new Date();

r = db.items
  .aggregate([
    {
      $match: { size: { $lt: 0.5 } }
    },
    {
      $lookup: {
        as: "owner",
        from: "users",
        let: { owner: "$owner" },
        pipeline: [
          { $match: { $expr: { $eq: ["$_id", "$$owner"] } } },
          {
            $lookup: {
              as: "partner",
              from: "users",
              let: { partner: "$partner" },
              pipeline: [{ $match: { $expr: { $eq: ["$_id", "$$partner"] } } }]
            }
          },
          { $project: { partner: { $arrayElemAt: ["$partner", 0] } } }
        ]
      }
    },
    { $project: { size: 1, owner: { $arrayElemAt: ["$owner", 0] } } }
  ])
  .toArray();

// printjson(r[0]);
// printjson(r.length);

print("Aggregation 2:", new Date() - before, "ms");

before = new Date();

r = db.items
  .aggregate([
    {
      $match: { size: { $lt: 0.5 } }
    },
    {
      $lookup: {
        from: "users",
        localField: "_id",
        foreignField: "items",
        as: "owner"
      }
    },
    { $unwind: "$owner" },
    { $project: { "owner.items": 0 } },
    {
      $lookup: {
        from: "users",
        localField: "owner.partner",
        foreignField: "_id",
        as: "owner.partner"
      }
    },
    { $unwind: "$owner.partner" }
  ])
  .toArray();

// printjson(r[0]);
// printjson(r.length);

print("Aggregation 3:", new Date() - before, "ms");

const find = (col, q) => col.find(q).toArray();
const byId = arr =>
  arr.reduce((a, b) => {
    a[b._id] = b;
    return a;
  }, {});
const fieldVals = (arr, field) => arr.map(a => a[field]);

before = new Date();

const items = find(db.items, { size: { $lt: 0.5 } });
const itemsById = byId(items);
const itemIds = fieldVals(items, "_id");
const users = find(db.users, { items: { $in: itemIds } });
const partnerIds = fieldVals(users, "partner");
const partners = find(db.users, { _id: { $in: partnerIds } });
const partnersById = byId(partners);
users.forEach(u => {
  u.items.forEach(i => {
    itemsById[i].owner = u;
  });
  u.partner = partnersById[u.partner];
  delete u.items;
});

// printjson(items[0]);
// printjson(items.length);

print("Find:", new Date() - before, "ms");

before = new Date();

print("\nMatch only");

r = db.items
  .aggregate([
    {
      $match: { size: { $lt: 0.5 } }
    }
  ])
  .toArray();

print("Match:", new Date() - before, "ms");

before = new Date();

r = db.items
  .find({
    size: { $lt: 0.5 }
  })
  .toArray();

print("Find:", new Date() - before, "ms");

before = new Date();

print("\nMatch + lookup");

r = db.items
  .aggregate([
    {
      $match: { size: { $lt: 0.5 } }
    },
    {
      $lookup: {
        from: "users",
        localField: "_id",
        foreignField: "items",
        as: "owner"
      }
    }
  ])
  .toArray();

print("Match:", new Date() - before, "ms");

before = new Date();

{
  const items = find(db.items, { size: { $lt: 0.5 } });
  const itemsById = byId(items);
  const itemIds = fieldVals(items, "_id");
  const users = find(db.users, { items: { $in: itemIds } });
  users.forEach(u => {
    u.items.forEach(i => {
      itemsById[i].owner = u;
    });
    delete u.items;
  });
}

print("Find:", new Date() - before, "ms");