People always ask "what causes lag?"
Well here is the short answer first, "everything causes lag".
Another common question is "How do I get rid of lag?"
Short answer here is, log out.
Not liking the answers so far are you? Well, let's try the not so short answers.
So what does cause lag? Well sorry to tell you but the short answer still applies. Everything causes lag. However, it is more a matter of how much lag is acceptable to you.
As for what you can do to get rid of lag, that depends on what type of lag it is.
First of all let's talk about the three different types of lag.
LAGMETER 1
You can use the lag meter (found in the Avatar Menu, Avatar Health sub-menu) to help determine which of these three is affecting you the most.
More detailed information is available in the Statistics Bar, which may be accessed by pressing Shift-Ctrl-1.
STATISTICE BAR
Network Lag
This is when you have connectivity issues. There are problems somewhere in the network between your computer and the LL servers.
Symptoms of a poor connection can include (but are not limited to):
Failure of your avatar or textures to rez;
Object information not displaying in hover tips when you mouse over them;
Teleport failure;
Random crashes.
Cumulative packet loss shows a percentage of data that is lost or failing to be delivered. It's in Help menu > About Firestorm, on the bottom line of the first section. It looks like: "Packets Lost: 760/302154 (0.3%)."
Realtime packet loss can be seen in the Statistics Bar, which may be accessed by pressing Shift-Ctrl-1.
Packet Loss: This shows the real-time packet loss. Lower is better, and infrequent spikes may be expected. If it stays high for a long period of time you will experience lower performance.
For some things, looking at real-time packet loss will be useful, like watching for lag when you do something or go somewhere; for checking your overall network performance, cumulative packet loss is more useful.
Also, check Ping Sim. Ideally, this should be under 200 ms. 400 ms is actually what Linden Lab considers too high. This is also known as latency.
If you're experiencing wildly high ping times, ask others nearby if they are as well. If no one is nearby, ask a friend, or ask folks from the group to come by.
If you all see high ping times, it is a server issue, and the region should be restarted.
You can try to mitigate network lag by playing with your bandwidth. Too high or too low (although we do find that too high can be a lot worse than too low) a value will result in network lag.
For information on how to determine your optimal bandwidth, refer to http://wiki.phoenixviewer.com/fs_speedtest
We generally recommend the following as MAXIMUMS (Think that is enough stress on maximums?):
Wireless: 500 (This includes a home wireless connection, i.e., a wireless modem/router.
Hardwired DSL: 1000
Anything faster (cable, fibre, etc.) again hardwired: 1500
Aside from the network issues mentioned above, some programs may inhibit or interfere with a good connection.
Some firewall software and anti-virus programs are known to do this. You may want to temporarily disable them and see if the situation improves.
Client-Side
Everything you see has to be drawn by your graphics card. When there is too much to draw, and your computer cannot keep up, you experience client-side lag.
Avatar Render Weight (formerly known as ARC - Avatar Rendering Cost) is part of client-side lag, as the name itself says.
Symptoms of client-side lag include jerky or sluggish movement.
There are many things you can do to reduce this, without having to ask people to adapt to you. Generally speaking, the better you make SL look, the more client side lag you will have.
Reduce your draw distance (do you really need to see 512m away?). One thing that most people do not realize is that if you double your draw distance you are actually rendering up to eight times as much area.
Be sure that Avatar Impostors is enabled (this makes drawing of distant avatars much faster).
Reduce the number of Max Avatars.
Both of these last two options are in Preferences > Graphics > General sub-tab.
Disable Atmospheric Shaders (which serves to drastically reduce how much your computer has to render, as the sky alone is very graphics-intensive);
If need be, inhibit the rendering of other avatars: Advanced Menu > Rendering Types > Avatar (just remember to turn that back on afterwards) or derender them.
Client-side lag is local to you. It is a direct result of how powerful your computer is. It is no one else's fault if your computer cannot handle a specific situation. So if you're in a high-lag setting, adapt temporarily as described above.
It must also be pointed out that client-side lag neither affects nor is affected by things like scripts, at all. It has next to zero impact on a sim's performance.
Particles
Contrary to popular belief, particles do not "lag a sim". Their effect on a sim, on the servers, is in fact close to zero. Particles are almost entirely client-side.
They are rendered on your computer, by your graphics card, and in fact do NOT require a script to keep them going.
They need a script to initiate the effect, yes, but afterwards the script may be removed and the particle effect will keep going forever - until another script is dropped in to turn them off, or the object is taken or deleted.
If you find that particles are "lagging you", stop it yourself, on your own computer. That way others who are less affected may continue to enjoy them.
You can disable particles in a number of ways:
Advanced Menu > Rendering Types > Particles
Preferences > Graphics > Max. particle count - set to 0
Server-Side
Server-side lag is caused by several things, independently. There are two major causes; all others are secondary and negligible. They are, in order of impact on a sim:
Physics. People, even wearing nothing at all, with the minimum possible Avatar Render Weight (1000) and no scripts, will lag a sim.
The sim needs to keep track of where each avatar is, to prevent them walking through one another, floors, walls, etc.
Every time your avatar moves it "collides" with something other than when you are flying or sitting, and each "collision" gets calculated on the server, thus creating more lag.
Sitting down reduces this lag significantly. Your avatar, in fact, becomes linked to the prim you're sitting on.
Scripts. This is common knowledge, compared to the previous point. If you know you're going to a busy event, then remove scripted attachments, as many as possible.
While there is no good reason whatsoever for anyone to be carrying around more than 200 scripts on a human avatar, even when in full RP attire, with combat HUDs, it is important to note that the number of scripts does not tell the whole story.
The amount of time a script uses is more important.
Contrary to popular belief, prims do not lag a sim - or more precisely, their effect on lag is minuscule compared to the two things mentioned above.
Scripted prims cause lag; unscripted ones do not - relatively speaking, of course.
So, if you're going to an event, before you leave for it, check your attachments (hair, shoes, etc) to ensure that they are unscripted. To those running events, it is strongly suggested that you ask attendees to do these things; a badly lagged sim affects everyone at the event.
NOTE: As stated earlier, lag caused by physics (primarily avatar movement) is the number one cause of region lag. If physics lag is bad enough, scripts simply will stop running; avatar movement is considered more important than scipts.
If there are 40 people at an event, and many are moving about, it will be laggy even if none of those people are wearing scripts.
NOTE: Moving away from a scripted prim will not do anything to reduce the "lag" it may be causing you. Scripts all run on the region server, and therefore, they are "global" to the server.
No matter where you are in the region, the effect of that script running - that is, the time taken to run it, and the memory it consumes - will be felt on the entire region.
It must be stated that this material is a simplification; the true situation is far more complex, but the intent was to be brief, simple, yet sufficiently correct.
This info is also available on our wiki page on lag - http://wiki.phoenixviewer.com/lag. For more detailed explanations, see the following web pages:
http://analutetia.com/?p=7191
http://gwynethllewelyn.net/2008/02/16/lag-myths-dispelled/
http://wiki.secondlife.com/wiki/Help:Lag
http://wiki.secondlife.com/wiki/Reducing_lag
http://wiki.secondlife.com/wiki/Statistics_Bar_Guide
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