Saturday, 22 November 2014

Why good matchmaking requires enormous player counts

Good matchmaking is an important part of creating an online multiplayer game. One thing you may not realise is that no matter how you build it, truly good matchmaking requires enormous numbers of players. Awesomenauts often has well over 1,000 people playing the game at the same time, which is very high and successful for an indie game. It certainly sounds like a lot to me, but this is only a fraction of what would be needed to do everything with matchmaking that we would want to do. Today I am going to explain why tens of thousands of concurrent players are needed for truly awesome matchmaking.

Matchmaking has two main goals. The first is to let people play together who will have a good internet connection to each other. We would like to avoid Australians playing together with Europeans because their ping will be very high. High ping decreases the quality of the game experience, especially in a fast and highly competitive game like Awesomenauts. Finding good connections is more complex than simply looking at distance: sometimes you have a worse connection to your neighbour than to someone on the other side of the continent. The internet is just very unpredictable and random when it comes to connection quality.

The second main goal of matchmaking is to let people play together who have similar skill. There is no fun in getting beaten by someone who is way better than you, and n00bstomping gets old really quickly as well.

Now that we know our core goals, let's try to estimate how much 1,000 concurrent players really is. I am going to simplify things and use a lot of assumptions, but I think the ballpark figures are realistic enough to communicate my point.

The first step is to look at how often these players are actually available for matchmaking. An Awesomenauts match takes on average somewhere around 20 minutes, so players are available for matchmaking once every twenty minutes:

1,000 / 20 = 50 players per minute

We don't want to matchmake with people who are too far away, and players are spread all over the globe. Let's say that the average player would have a good enough connection to one third of all players. In reality players are not spread equally, since Awesomenauts is more popular in some countries than in others, and because of time zones. Let's work with that one third though:

50 / 3 = 16.7 players per minute

Next step is skill. Let's say we consider one third of all players to be close enough in skill to make for a fun match:

16.7 / 3 = 5.6 players per minute

AUCH! We are already down from 1,000 concurrent players to only 5.6 suitable players per minute, and this is while looking at only the most basic of assumptions...

For perfect matchmaking I would want to split players further. A common request from Awesomenauts players is to have unranked and ranked multiplayer. If we would add this, the split between these modes would probably not be equal: one mode would likely get more players than the other. Let's assume one third of all players would play one mode, and two thirds would play the other mode. We need to split further from the already small numbers we have because even in unranked matchmaking we still want to match players based on similar skill to create fun matches. This is how few players we would have left in the smallest of the two modes:

5.6 / 3 = 1.9 players per minute

Another common request from the Awesomenauts community is to split pre-mades from solo-queuers. A pre-made is a group of people who form a team by hand in the lobby before the match, while solo-queuers are put together in a team with complete strangers by the matchmaker. Pre-mades potentially have a big advantage because they will likely do much better teamwork. In the ideal case pre-mades would therefore only play against other pre-mades. How many pre-mades there are varies wildly with the skill level of the players (highly skilled players generally play in pre-mades much more). Let's assume that on average one fourth of all players are in a pre-made:

1.9 / 4 = 0.46 players per minute

Since we are talking about perfect matchmaking, let's have another look at our skill-based matchmaking. Above I assumed that one third of all players is a good enough match in skill. In reality the top players are way too much better than the rest to make this ideal. The top 5% of players are an enormous amount better than the top 33% of players. The more precisely we could match based on skill, the better. I think we would need to do at least three times better than we did above for ideal matchmaking:

0.46 / 3 = 0.15 players per minute

I can imagine some more criteria for ideal matchmaking (like supporting more game modes in matchmaking), but I think the point is quite clear already. With 1,000 concurrent players it will take 30 minutes to fill a match! Obviously this is totally unacceptable. Here's a summary of all the criteria I have mentioned so far:



Let's say it is fine to let players wait for two minutes for a match to fill up, bringing us to 0.3 suitable players during the available time for matchmaking. To bring us to the required 6 we would therefore need 6 / 0.3 = 19 times as many concurrent players for good matchmaking. We started with 1,000, so we need 19,000 concurrent players. Of course there is a big daily fluctuation in the number of players (there are fewer players deep in the night and early in the morning), so to also have good matchmaking at the slow hours we would need three times more players still. Thus we would need 58,000 concurrent players at peak for good matchmaking. That probably equals over 5 million unique players each month. Holy cow that is a lot!

When building a multiplayer game it is important to think about this. Ideal matchmaking requires enormous player counts, and if your matchmaking is built assuming such player counts will be there you might make something that works really badly for more realistic numbers. Therefore the ideal matchmaking system is flexible: it brings perfect matchmaking when there are tons of players but also makes the best of a small player count.

Despite all of this we can still make big improvements to the matchmaking system in Awesomenauts. We are aware of this and are therefore rebuilding the entire matchmaking system from the ground up in a much smarter and much more flexible way than is currently in the game. I am sure this will bring a big improvement, but at the same time it is important to have realistic expectations: no matter how well we build our matchmaking, the player count required for 'perfect' matchmaking is unrealistic for all but the few most successful games in the world.