Meteor pub-sub test.

pub-sub.js

// demonstrates how the local MiniMongo collection will only hold the required data necessary to fulfill 
// queries on the returned data from the publication and that sort order is not prerserved, only the backing data

// tmp test
import {Mongo} from 'meteor/mongo';
import map from 'lodash/map';

console.log('start');

const Foos = new Mongo.Collection('foos');


if (Meteor.isServer) {
  let counter = 0;
  Foos.remove({});

  Meteor.setInterval(() => {
    counter++;
    Foos.insert({val: counter, timestamp: Date.now()});
    console.log('counter', counter);

    if (counter % 10 === 0) console.log(Foos.find().length);
  }, 1000);

  Meteor.publish('vals', function ({sortOrder = 1}) {
    return Foos.find({}, {limit: 10, sort: {val: sortOrder}});
  });
}


function allVals() {
  return map(Foos.find().fetch(), 'val');
}

if (Meteor.isClient) {
  subscribe({sortOrder: 1});
  window.getVals = printVals;
  window.subscribe = subscribe;
}

let handle;
function subscribe({sortOrder}) {
  if(handle) handle.stop();
  handle = Meteor.subscribe('vals', {sortOrder});

  Tracker.autorun(() => {
    console.log(allVals());
  });
}


function printVals() {
  const vals = allVals();
  const max = Math.max.apply(Math, vals);
  console.log('val max', max, 'val count', vals.length, 'last ten',vals.slice(0, 10));
  window.vals = vals;
  window.map = map;
}

console.log('end');

By calling subscribe({sortOrder:-1}) you will see that your local collection at times is 20 elements, not 10, with a mix of sorted and unsorted content. Also try a call with sortOrder: 1 to see it toggle back to a 10 item collection.