Talk:Project Motivation

Scaling for events

I would like to add more scary numbers to the main namespace here.

• If N people are interested in an event today, and the population grows tomorrow by a factor of M, then tomorrow N*M people will be interested in that event, assuming unchanging population demographics.

• Every live music event by the top few SL musicians maxes out their event sim: let's assume that this means 100 people, although the demand is undoubtedly higher already but not satisfied. SL currently has just under 10m registered residents. If the scary number for total population size is 2 billion, then the scary number for event interest is 100*2000/10 = 20,000 to an event region, given unchanging demographics.

• Of course, worldwide we do not have an unchanging demographic, but no matter by how much you want to reduce this figure as a result of this, the answer is still collosal. And bear in mind that there is much uniformity in eastern populations, just as there is in the west, so event interest within each cultural domain will be huge. And of course many events are cross-cultural.

• Which brings me to the issue that nobody seems to want to tackle: the new architecture needs scalability for events.

• While I recognize fully that there are monumental hurdles in the way of achieving this, it is just an engineering problem with a number of known partial solutions and amenable to tradeoffs. Worse, not addressing it will leave us exactly where we are today, with zero scalability for events. And, very unhappily, SL will become the virtual world where almost everybody is barred from their favorite event. 19,900 people out of every 20,000 will have to stay at home. That's not the future system we want to build, in my view.

• Please add at least 10,000 per region to the scary numbers, to focus the mind. --Morgaine Dinova 21:07, 24 September 2007 (PDT)

• I mentioned this at Zero's Office Hours today, but no traffic yet, so added it myself. --Morgaine Dinova 17:42, 25 September 2007 (PDT)

Zha's comments on events

The event discussion came up at the AWG kickoff, and comes up from time to time in Zero's office hours. At the heart of the event discussion is the desire to host very large events inside the SecondLife environment. This raises the question, what will 200, 500, 1000, 10,000, 20,000 users be able to do in a single contiguous portion of second life space. Assuming for a moment, we could manage the simulator side space, what would a client see? At 100 avatars in a sim, my current screen is pretty much solid avatars with a cloud of tags floating over them, all in constant motion. (Granted we're also all in concrete, in the current sims, but we'll assume that can be fixed.)

Somewhere north of 500 avatars, I can't see how I could render more than a fraction of them, nor could I interact with more than those I could see right near me. So, and I am quite serious about this question, what are we attempting to achieve. If the answer is "let us all share the stream" I'll point out that the streams are orthogonal to SecondLife. If it is interactivity, in the current style of SecondLife, I'd like to see a use case for how we could produce an interesting user experience with the number of avatars I listed above in ear shot. How fast will the chat window scroll? How fast will people's "nearby" windows update? How many avatars do we expect our scripted objects to be able to sense, and how will we even see most of the avatars

Beyond the user experience, we also should look at some hard technical questions. How many Kbits per seconds of updates are needed to support each of these size points? Can we get that from current networking hardware. Look at these questoins, Simulator to Client, Simulator to adjacent Simulators, and Simulator to utilities, and agent domains.

This isn't a simple "let's quash the idea" post, far from it. But If we are asserting this as a desire, lets actually produce some use cases which describe what we are trying to enable. "20,000 in an event" isn't a requirement I can design against. Give use some use cases which describe the actual user experiences that we wish to enable. Look hard at questions like "How will chat look, how will visibility work, how would scripting behave." Capture these in use cases.

I will suggest, for example, that some use case can be solved by better inter-region behavior. Others, would only be solved by attempting to limit the interactions between avatars in significant ways. Serious discussion, backed by used cases, would be invaluable here.

- User:Zha Ewry 9/25/2007

Morg's reply to Zha

Hooray, comments at last. :-)

• Good, let me start off with a serious but not particularly helpful response in the form of a rebuffal: we have 20k-100k+ people events in RL taking place every weekend in thousands of places worldwide, and it seems to work just fine. So, we know that it can work in the physical world, and that it is a very human thing to do. And the 3D virtual world is to a very large extent a recreation of physical space, but with added capabilities, so this is both desireable for people and natural in a virtual recreation of physical space. The only problem is that it's hard to do, and it's not on a well beaten trail.

• Seen in that light, the question I want to entertain is "How can we achieve this?". I don't feel the need to defend the desire for it, and anyone who follows the SL live music scene and is hitting their head daily against lack of scalability for events would I'm sure express that same feeling just as forcefully. It's a bad state of affairs, and it needs fixing, particularly in the context of an ambitious project that addresses all other areas of scalability. Let's just do it. (In stages of course.)

• Now to answer your questions specifically:

• What will 20-20,000 users be able to do in a single contiguous portion of SL space?

Exactly what they do in RL. Sit in seats in stadia. Gather in crowds at rallies and concerts. Roam in the park in smaller groups. Join hands in a 2000-person line dance. Sky-dive in 500-person snowflake patterns. I don't know, anything. That's up to them. I really don't think we need use cases for this. Just open the curtains or turn on the telly for use cases. :-)

• What would a client see? ... Somewhere north of 500 avatars, I can't see how I could render more than a fraction of them.

First of all, let's not be hung up on the current client. This will change drastically, and in any case there will be umpteen different clients, each suitable for a different purpose. (It's one of the reasons why I'm trying to partition the graphical part into an independent front end, so that viewing can be modified easily without impacting the rest of the client that is mainly concerned with communications.) No doubt this will include crowd-capable clients as well ... if region scalability allows a crowd to gather in the first place.

So, the client would see exactly what a person sees in a crowd in RL, but much more flexibly. Numerous options for this have been explored in the SL forums, from simple reduced detail rendering, rapid-falloff CLOD, to performance-driven culling, and selective viewing. Unlike in RL, you could select to render only those in your group, or only furries, or only pretty girls (OK, that's not much of an object reduction :P). Many people have suggested that ghost outlines would suit them just fine, and even more want a GuildWars-type "Observer Mode" in which their avatars are not rendered at all for others to see, which would reduce the problem substantially if it proved popular. So, there are lots of options.

• nor could I interact with more than those I could see right near me.

And nor would you in RL, unless you're shouting, so this works pretty accurately. It would however be much easier to interact with your friends here since you could make everyone else disappear. Fortunately sound volume already falls off with distance in SL so that part of interaction is covered. Reading vicinity text scroll is clearly not viable in crowds, so this would need to be filtered in some manner chosen by each person, such as by group membership or friends only, or by distance just like sound. None of this is hard.

• How many avatars do we expect our scripted objects to be able to sense?

This is actually a much more interesting question than the others. Even with the huge improvement that Mono will bring about, it's going to need more than faster LSL processing to do a good job in this area. It's going to require substantial improvements in sensing functions, and probably some language assist in the form of proper O(1) indexible arrays (at long last). But then, land owners have been crying out for better sensing functions for ages. It's time for it.

I think I've answered your questions in debating style Zha (the questions were in that style too), but the detail has to be tackled far more precisely of course, and I'm ready for that. At this stage though, I'm looking merely for acceptance of the basic premise. I don't want to be on the defensive, as if this one area of scalability were somehow taboo. And that's how it has seemed over these past 3+ years. :-) --Morgaine Dinova 19:43, 25 September 2007 (PDT)