About Second Life Simulator 1.20.83683 (Havok4 FAQ)

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This article is part of the Second Life® Knowledge Base. Although Linden Lab can't guarantee its accuracy, as part of the Knowledge Base it must meet high quality standards, and designated reviewers must approve any changes.

This article, originally a post on the Official Second Life Blog, discusses the following topics:

• A brief overview of the rollout of Second Life Simulator 1.20.83683, which includes an update to the inworld physics engine to Havok4
• How to file a Havok4-related bug in the public issue tracker (JIRA)
• Some frequently-asked questions about Havok4 and its effect inworld

Overview Of Results

The deployment of the new Second Life Simulator v1.20.83683 was completed early in the morning of April 2, 2008. Overall, the process went smoothly, and the general reports we have gotten are positive. We also learned some things in the process, and we wanted to take this opportunity to pass on some information about where we are and what our next steps look like, and to provide an opportunity to hear more feedback on the update.

We discovered partway through the update process that the deploy script in use had not been updated to incorporate a bug fix. We apologize for the inconvenience of having a "no notice restart" for those who were affected by this issue. For the first part of the rollout, simulators were being shut down and restarted with the five minute restart warnings. As soon as this issue was realized, the deploy was halted, we picked up the fixed version of the deploy scripting, and continued from that point.

Some regions have found unexpected behaviors, and as posted before the deploy, we expected that this would happen. Even with a large scale beta test, we still know that we could not test everything that has been built across all of Second Life.

If we could ask for one thing, and only one, it would be "If you see something misbehaving after the update, please do not panic! Report it as a bug -- as described below -- and we will work through the list and deploy a set of updates over the next few weeks with issue resolutions as soon as we can."

Many of the issues found have already been addressed and others are being worked on. We are here and continuing to work through issues as they are discovered, so please do not assume that "this is it" -- the team is still working through the new issues uncovered by bringing the new simulator to all of Second Life.

Did We Test Everything In Second Life? Is That Even Possible?

As mentioned in earlier blog posts, although we ran an extensive and long public beta program, we know that not every vendor opted-in to participate and not every product could have been tested. Some products have been found during the rollout that are not working correctly, and we are working to resolve issues as we become aware of them.

Please remember that if you find something that does not work with the new simulator, the best way to handle this is to let us know about it. We can and will work to try to resolve issues that we know about, and all we ask is that you take up your part of this process, and report the issue in the public issue tracker at http://jira.secondlife.com.

How Do I Report A Simulator Problem?

1. Open http://jira.secondlife.com, and log in with your Second Life login credentials.
2. Click Create Issue.
3. In the Project dropdown, select 2. Second Life Service - SVC.
4. In the Issue Type dropdown, select Bug.
   
5. Click Next.
6. Type a one-line description of the issue in the Summary line.
7. Explain the details of the issue in the Description field. Please include the following:
   • The name, version and creator of any product involved in the bug.
   • The location where the bug occurs (for instance "Ahern 128,128,0").
   • A step-by-step description of how to make the problem appear. Please assume that we do not know how to operate products that you own, as we may not have seen the particular item before, and if you can help us to focus on the bug fix rather than learning a product, we can get the fix done faster!
   • Which viewer were you using when you found the bug? To find this information, go to the menus at the top of the Second Life window and select About > Second Life. Copy the first text line and paste it into the text box.
8. In the Component list, select whatever seems to best fit -- typically Physics, Scripting or Performance.'
9. Click Create at the bottom of the form.

Common Questions and Issues

Q: I've heard that there are new rules that govern how prims are linked in the new simulator. Where can I find more information on this?

A: http://wiki.secondlife.com/wiki/Linkability_Rules

Q: Ok - that linkability rules page makes no sense to me! Can you explain in plain English what the linkability rules are about?

A: (Long one; sorry, this is actually the shortest answer we could think of!)

Whether prims are linkable in Second Life has always been governed by formulas. The Havok1 formulas were based on a "cube model," where things had to fit within the cube to link. The problem with that model is that if you rotate the item on rez, things at the extreme boundaries would fall off and be non-linkable.

The new model is based on a sphere, so that no matter which orientation the item is rezzed in, the previously linked parts will still link.

The rest of the details of "how many", "of what size" and "how far apart" are mathematical formulae that are by nature interrelated. If we were to simplify them into a sentence or two, we'd get avalanched by people who say "well here's an example that doesn't match the rule", which is why we've been less comfortable with a text Cliffs-notes version.

The bottom line is that things that used to link in the old simulator should link in the new one. If you build something in the new one, it might not link in the old one. However, that issue now becomes moot as we roll out the new simulator to the whole Second Life system.

Q: I am seeing performance problems on my region that didn't seem to be present before the update. What could be causing this?

A: There are a few types of operations that seem to cause more performance impact with the new physics engine than the old one. In particular very complex shapes that are rezzed repeatedly and quickly can take more of a toll on performance than with the old simulator.

Products that we have seen create this problem include:

• Some (not all) fish rezzers
• Some (not all) wave generators
• Some (not all) special effects generators
• Some (not all) vehicles, in particular complex vehicles

If you are seeing lower performance on your region after the update, please check the following things first:

1. If you are the region owner, select World > Region/Estate from the menus at the top of the Second Life window. Then click the Debug tab. Click Get Top Scripts and then click the column header titled Time twice, so that the list is sorted with the highest time at the top. If you see one or a few rows at the top with script times that are much higher than the rest of the entries, these scripts may be responsible for much of the performance impact. In many cases, we've seen one or two scripts be reponsible for a large percentage of the performance issues. Often they are one of the categories listed above. As an experiment, try disabling or derezzing those high-script-time scripts, and see if the region performance recovers. If it does, please file a bug in the manner described above, naming those scripts and the numeric results, so that we can look at how to optimize for them -- or to talk to the builders to have them create an optimized version for the new simulator.
2. Watch the Time section at the bottom of the Simulator section of the Statistics Bar (hit Ctrl+Shift+1 on your keyboard) to see which time components are the largest, and which vary the most. If you see a clear pattern, please file a bug explaining the numbers you see here, along with any script findings above.

In a few cases, we have identified a single scripted item that is causing a performance problem, and been able to optimize for it without changing the product. In others, the product may need to be enhanced to be more efficient on the current simulator.

We know of a few regions that are having performance problems unrelated to a specific script, and are working with them directly to research the issues and find ways to improve performance on those regions.

Q: Why can I not climb up stairs that I could climb up before?

A: The new simulator uses a more realistic avatar climbing model. It uses a location at about the standard-height knee point as the height of barrier that is considered to be a "wall" for avatar stair climbing behavior. If stairs are too tall, the avatar will not be able to climb them.

Q: Why are some vehicle very fast on the new simulator?

A: After many weeks of discussions with vehicle builders, it was decided to raise the maximum "script motor speed" in Second Life to 256 m/sec. This is far faster than the previous motor limit. In order to "get around" the previous lower limit, some vehicle makers would add impulse pushes to the vehicle, which could force it to go faster than the motor speed setting. Now, with the higher motor limit, you get the max motor speed plus these extra pushes, which in some cases can result in a very surprising top speed.

This is a case where the community spoke clearly in office hours and other discussions, and the builders said that they wanted to be able to do better vehicles in the future, with better motor control, and would live with the idea that some existing vehicles might have speed problems. Some vendors are planning to do updates that will be tuned specifically for the new motor characteristics, and others are release whole new product lines to take advantage of these relaxed limits.

Q: I have some other product that is not behaving after the update. What should I do?

A: The first thing to do in this situation is to contact the vendor who makes the product. In many cases, their current version will work fine with the new simulator, or they are planning an update that is tuned to the new simulator's behavior.

If the product vendor has an issue or bug that needs fixing in order to get the product working correctly, please encourage them to file a bug to explain the problem, get involved with the development team, attend office hours, or otherwise let us know what the problem is and what sort of resolution would be helpful. The Havok4 team will be continuing to fix these issues for the next several weeks directly, before turning the simulator over to ongoing support.

Q: I am a product vendor, and my product does not work correctly on the new simulator. What should I do?

A: Please file a bug describing the problem behavior, and if possible, include a sample simplified script to demonstrate the issue (so that we don't have to pick through thousands of lines of your code to find the 20 lines that illustrate the bug). If sample code is not possible, we will work through the existing product to figure out the issues, but it will take longer to resolve problems this way.

Please attend office hours if you can, so that we can talk directly about any issues and discuss how to best resolve them. Office hours are held at the center of "Content to Hover" on Tuesdays at 11:00-12:00 PST and Thursdays at 17:00-18:00 PST.