Further, a listen causes no perceptible lag, it is the chat that wakes up the listen. If you are listening on a channel no one is chatting on you do not wake up. Scripts can start to create lag when they cause physical events to happen that effect the server.

There is a lot of folklore about lag in the educated circles. A simple coding mistake in the server code that causes a pruning operation to not prune where it can can have significant effect. Scripters may learn of this by trial and error and then “fix” it in their scripts, after which, Linden Labs fixes the root problem and all those fixes are not needed and it turns out there was no lag from the scripts in the first place.

You may guess I am a scripter. People tell me I am a very advanced scripter. I also an a software architect, operating systems designer, and many other things. I do not know how the servers at Linden Labs work. I am sure then can be improved, almost all software can be.

There are some bad scripts out there that waste resources, but by in large, they are hurting other scripts.

“Second Life and can only be repaired by replacing your modem or having your ISP fix the problem.”

I worked for a major ISP and also for a networking company. Phone your ISP if you like to complain about performance — but apart from helping optimize your computer — there’s a good chance they won’t help. Except for the modem — which likely isn’t the bottleneck — they aren’t going to replace or tune their network performance to suit you. (The guy down the street has 30% better performance from the same company — sometimes that’s just the way it goes — they’re closer to a headend, etc.) A very common misconception is that your own computer plays no part in network lag. It’s very unfortunate that people believe this is true. Buying a faster overall computer will have a dramatic effect on download and upload speed. Buying a better network card, alone, is likely to help.

The Avatar Rendering Cost (Advanced Feature) is excellent to determine how performance-intensive hair is. A friend increased her FPS by 15%, just by switching to a style with fewer flexi prims. But also, you aren’t helpless — the perfomance of your favorite doo can be improved by editing individual pieces that don’t need to be flexi, or transparent. I reduced my Avatar Rendering Cost by 900 (25%) — but it took two hours of editing.

For the typical user, a big factor is who else is sharing the server. I’m not sure how SL shares a RL computer between sims, one person said it’s 4 sims to a server, another said it’s 1. The easiest optimization is to pick a property that’s fast.

I can speculate that the physics engine optimizes by using some kind of branching tree of smaller and smaller subsections of the region so that it can calculate based on a smaller number of prims at a time. If that is the case, prims that are very large might prevent the system from being to branch into as many smaller sections, forcing the simulation to consider larger numbers of prims at one time, this making the simulation much slower.

That’s just a guess.

GIven how well the vendor scripts worked at the Fair, it is obvious that you took great pains to minimize them. While it is true that the main form of lag people were experiencing at the Fair, the inability to move, could not be caused by scripts, scripts can be hindered by that form of lag so keeping the scripts small, simple, and efficient means that they can operate with reasonable reliance under such adversely laggy conditions. Despite all of the lag, I only had two people report a problem purchasing something with a vendor from me, at Hair Fair 2009.

I can assure you that I did my very best on that front! There’s no Listen calls, no timers, no loops, and certainly no detection or collisions used. Scripts I built for the HF vendors and donation kiosks are only active when someone buys something, and the transaction lasts a few seconds. The only overhead is that they do a HTTP request on the HF accounting server, to log transactions. But that was absolutely needed as a feature for tracking accountability.

Very very good article, kudos!