Analytics: minor segmentByChannel improvements

[Ivshti]

Minor changes, such as:

• not using mutable objects to simplify the query
• increased MAX_LIMIT
• segmentByChannel can be used in any case now
• researched perf impacts

Attaching a report regarding perf impacts:

const measure = x => {
	const n = Date.now()
	return [
		db.eventAggregates.aggregate(x).toArray(),
		Date.now() - n
	]
}

// Wrapping time in an object in _id
measure([{"$match":{"created":{"$gt":new Date("2020-01-11T22:30:45.897Z")}}},{"$project":{"created":1,"channelId":1,"value":{"$toLong":"$totals.CLICK.eventCounts"}}},{"$group":{"_id":{"time":{"$subtract":[{"$toLong":"$created"},{"$mod":[{"$toLong":"$created"},60000]}]}},"value":{"$sum":"$value"}}},{"$sort":{"_id":1,"channelId":1,"created":1}},{"$limit":100},{"$project":{"value":"$value","time":"$_id.time","channelId":"$_id.channelId","_id":0}}])
// 3723, 4097, 3762

// Original query
measure([{"$match":{"created":{"$gt":new Date("2020-01-11T22:30:45.897Z")}}},{"$project":{"created":1,"channelId":1,"value":{"$toLong":"$totals.CLICK.eventCounts"}}},{"$group":{"_id":{"$subtract":[{"$toLong":"$created"},{"$mod":[{"$toLong":"$created"},60000]}]},"value":{"$sum":"$value"}}},{"$sort":{"_id":1,"channelId":1,"created":1}},{"$limit":100},{"$project":{"value":"$value","time":"$_id","_id":0}}])
// 4219, 3848, 3733

// no noticable difference


// With channel grouping
measure([{"$match":{"created":{"$gt":new Date("2020-01-11T22:30:45.897Z")}}},{"$project":{"created":1,"channelId":1,"value":{"$toLong":"$totals.CLICK.eventCounts"}}},{"$group":{"_id":{"time":{"$subtract":[{"$toLong":"$created"},{"$mod":[{"$toLong":"$created"},60000]}]},"channelId":"$channelId"},"value":{"$sum":"$value"}}},{"$sort":{"_id":1,"channelId":1,"created":1}},{"$limit":100},{"$project":{"value":"$value","time":"$_id.time","channelId":"$_id.channelId","_id":0}}])
// 5280, 5913, 5822
// some degradation


// With channel grouping - nonzero
measure([{"$match":{"created":{"$gt":new Date("2020-01-11T22:30:45.897Z")}}},{"$project":{"created":1,"channelId":1,"value":{"$toLong":"$totals.CLICK.eventCounts"}}},{"$group":{"_id":{"time":{"$subtract":[{"$toLong":"$created"},{"$mod":[{"$toLong":"$created"},60000]}]},"channelId":"$channelId"},"value":{"$sum":"$value"}}},{"$sort":{"_id":1,"channelId":1,"created":1}},{"$match": {"value": {"$gt": 0}}},{"$limit":100},{"$project":{"value":"$value","time":"$_id.time","channelId":"$_id.channelId","_id":0}}])
// 5684, 5348, 5595

// New query - w/o channel grouping but nonzero
measure([{"$match":{"created":{"$gt":new Date("2020-01-11T22:30:45.897Z")}}},{"$project":{"created":1,"channelId":1,"value":{"$toLong":"$totals.CLICK.eventCounts"}}},{"$group":{"_id":{"time":{"$subtract":[{"$toLong":"$created"},{"$mod":[{"$toLong":"$created"},60000]}]}},"value":{"$sum":"$value"}}},{"$sort":{"_id":1,"channelId":1,"created":1}},{"$match": {"value": {"$gt": 0}}},{"$limit":100},{"$project":{"value":"$value","time":"$_id.time","channelId":"$_id.channelId","_id":0}}])
// 3905, 3698, 3877