People use the term a great deal, but usually without really understanding what it means, what causes it or how to deal with it. Some of the things commonly suggested to reduce lag actually have little or no effect.
First off, “lag” is a catch-all word that actually covers three very different things, and it is important to distinguish between them. Most lag reduction methods only deal with one of these three aspects.
You can use the Statistics Bar to get detailed information of what might be causing lag.
This is when you have connectivity issues. There are problems somewhere in the network between your computer and the LL servers. This usually can be noticed when you start to experience packet loss. Press Shift-Ctrl-1 (or Advanced35) → Performance Tools → Statistics Bar) and look at the top, packet loss; ideally this should be 0%; if it isn't, you have a connectivity issue and are losing data. Also, check Ping SIM. Ideally, this should be under 200.
Symptoms of a poor connection include (but are not limited to):
You can try to mitigate network lag by playing with your bandwidth. Too high, or too low, a value will result in network lag. For information on how to determine your optimal bandwidth, refer to this page.
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.
Everything you see has to be drawn by your graphics card. When there is too much to draw, when 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:
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 does NOT affect things like scripts, at all. It has next to zero impact on a SIM's performance.
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 afterward 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”, it is wrong to ask that the effect be stopped. Instead, 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:
Doing any of these things will stop particles “lagging you”. There is no need to ask others to degrade their SL experience on your behalf. Also, again, particles do NOT cause server-side or script lag. Even if the scripts are not removed, a single one uses 0.02ms script time.
Owners of venues that have a “no particles” policy may mean well, but are misinformed. Again, particles do not lag a SIM, and are very easily dealt with client-side as described previously. Those venue owners are aiming at the wrong target in trying to reduce lag: particles aren't it, scripts are - and even more so, moving avatars (see below). You can't remove the avatars, of course, but you can request that they not show up with heavily scripted attachments.
(Having said that, every little bit helps when it comes to reducing script lag, so if you have a particle effect that does not require the script to be in it at all times, remove it.)
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:
Contrary to popular belief, prims do not lag a SIM - or more precisely, their effect on lag is miniscule 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 the above is a simplification; the true situation is far more complex but the intent is to be brief, simple, yet sufficiently correct.
For further information on lag, please consult the following: