Because Andrew Linden asked (and even though I note that only something like 50% of "Linden Answers" questions ever get answered), I will post about this issue one last time.
This will be my fourth thread about this topic with no answer or comment from Lindens besides a Torley "I'll ask someone to look into that," and I believe I have made two or possibly three detailed bug reports on it over the last year as well.
1) "Pulse Lag" is a freezing lag that occurs in spikes, usually on a rhythmic basis. Every four or five seconds, the entire interface and all action freezes for about one or one and a half seconds. It occurs irrespective of location or of objects in the visual field and makes second life almost unuseable for the sufferer. The last time I sent documentation to the bug hunters (pictures of the fast timers) I obtained it at 800 metres in the air in a completely empty sim. It is not related to complicated geometry in the area, number of avatars in the area, or large textures in the area. It occurs sometimes for days and days at a time, or sometimes for just a few hours. It comes and goes at random. I have experienced it on and off, (and I know others have as well) for at least 8 to 12 months although I did not complained about it at first as I was not technically knowledgeable enough to know that it was something unusual.
2) When you open the fast timers, you can clearly see the lag spikes as they go by, they are usually single bars that are five to ten times the length of the other bars. With the new display you can also see the lines in the graph along the bottom slowly rise up like an incoming tide until a huge lag spike peaks, everything freezes, and then just as quickly returns to normal for a few seconds before slowly rising up ready for the next spike. The spikes in the top part of the graph, (ostensibly) tell you what it is causing the lag but in this case it is many different things. For a while, the spikes will be primarily composed of "world updates" then one will perhaps be an "occlusion update" or an "image update" and then maybe back to a world updates again. As I have pointed out in previous posts it seems clear that this is network induced lag and that the makeup of the particular spike is merely what unfortunate process it was that was trying to complete itself at the point when the network froze.
3) The only other symptom, and the other clue that the lag is based on poor network performance of the SL software is that the ping readings are racing up and down the scale during a "pulse lag" episode. While I often get bad ping readings, and sometimes good, the user ping and the sim ping are typically very close to one another. During "pulse lag" episodes however, the user ping will be 4 while the sim ping will be 545, then the user ping will (in a second!) climb up to 230 while the sim ping will drop to 15. The numbers area always different but the fact that they race up and down a very large scale and usually at odds with each other is a major symptom.
4) While the obvious culprit is the network (despite many many denials that this is even possible from several Lindens and other "experts" on this forum), it is not *my* network that is at fault. I access Sl through a router and a local network ADSL service that other SL residents (my sister and my close friend) also use and neither of them experience "pulse lag" even when they are online at the same time as myself. I have no odd network settings in my SL installation and have installed and un-installed SL many times with default settings and various "tricks" that have been suggested to me all to no avail. It's not my network, or my settings, it's an issue with the way in which SL's code interacts with the network. i.e. - a bug
The only other real clue I have is that of the other people that have told me that they also experience this kind of lag, two of them had the same kind of computer as me (12" G4 laptop). It has been suggested to me by more technically inclined people than myself where I work that perhaps the "network stack" on this particular machine is interacting with the SL code in a different way than on other machines.
Even if I am completely wrong about this and my assumptions about its source, the fact that I have to scream and post and bug report something for six months to a year that is a serious problem and makes the game virtually unplayable for me when it happens is inexcusable. Why no one has nailed this problem down, nor even responded to me with a wild guess as to its cause, in all the time I have been complaining about it is a mystery to me and will remain so even if you solve the acutal "pulse lag" tomorrow.
