Megaprims and lag

We recently put up a platform megaprim on our sim -- something like 60x60x60 up at around 700m or so -- or it could be slightly smaller, I am not sure at the moment. In any case, later in the day the sim started acting wonky. Water disappeared, lag popped up -- when we shouldn't be lagging at all, we have only a few thousand prims on the sim so far and not very many active scripts either. The stat bar doesn't reflect a script issue, and in any case we were not lagging with the existing scripts prior to putting up the mega.

The disappearing water issue fixed when I restarted the sim, but the lag persists. Is that kind of lag typically caused by a prim of that size?

I know of a mainland sim that's loaded with megas up to 60m and a single mega hollow cylinder that's over 3000m long. The only lag I see there is client side, and mostly because of the huge use of particles and transparency. (^_^)y

Is the megaprim overlapping the sim edge at all? That may be the source of the lag. They interact badly with sim edges.

Try eliminating the mega, and see if the lag persists. If the lag vanishes when the mega does, then yes, that one mega was tyour problem. Simple enough to test.

Yes, megaprims can cause problems. They are, by deifnition, bugs. When you intentionally use bugs, you should expect buggy behavior.

This is especially true in situations in which megaprims interpenetrate other objects, because the simulator isn't quite certain how to process it. It can get even worse when physical objects collide with or interpenetrate the megaprim (and remember that avatars are physical objects as well). The absolute worst are when you have physical megaprims (two words that do not go together).


Megaprims are not officially supported by Linden Labs. As they are not created through official, documented means, they are prone to unexpected behavior. The simulator code is designed to process and deal with objects no more than 10mx10mx10m, when you ask the simulator to try to process objects that are outside of its normal operating parameters, it's going to take more time to try to figure it out. When the sim has to "stop and think," that's called lag.

Also if you are going to use Mega prims try to use the ones created in May this year rather than the old ones which were made with prim torture and have bounding box issues. I have a shopping centre builf from them in upto 70x70 and worst problem I have founfd is some people sink 6 inches into them when they teleport in, but this is easily fixed by adding a normal prim mat in your TP landing area.

I use megaprims in almost all my builds on my land in an open space sim and have not observed any lag resulting from their use whatsoever.

If it is your sim you can check for colliders by using the estate tools. Although mega prims that are "solid" used to be prime sources of lag, I understand that Havok 4 can deal with them fine now, but maybe I got that wrong.

Either way, I would not use megaprims, solely on the principle that you don't get something for nothing. If there was no issue, LL would (presumably) release a viewer with an increased limit on prim size.

But I think the sole remaining *known* issue is the parcel encroachment problem, which is supposedly being addressed in an upcoming release, for all prim sizes. It's not surprising that megaprims are particularly subject to this problem because they're so darn big it's just easier for them to encroach very dramatically.

Of course, part of the reason this happens so much is that we can't create them ourselves in the Editor, so we use (or make) carved-up hunks of what megaprims do exist; often the origin of those prims and the coordinates of their carved bounding box are not so easily found--so they end up somewhere other than where they belong.

They're working on it. The last necessary thing they need to do is not so much a technical requirement as a social one: they're working on being able to return an object which overlaps your parcel but does not have its center over your parcel. Obviously this is one of the big social problems with megaprims, it is not a technical problem related to lag.

Yes, yes - this makes sense! Duh - and it was an obvious reason too - thanks Qie!

/me slaps his own forehead

In general, megaprims do not cause lag by themselves, but can cause lag in very specific circumstances (such as the interpenetration situation described above). I've used them on the mainland as well as on private estates, and never once have I had any problems related to lag or simulator stability, but then I am very careful how I build normally anyway.

Like anything else, particles, textures, scripts, etc, improper use can cause problems.

That said, LL does have a small laundry list of what they consider are "showstopper" issues with releasing megaprims for general use, including some social and some technological issues (one of them being problems with the minimap). Andrew Linden said they do have it on the road map to have these issues resolved by the end of the year, though, so expect megas to become standard in just a few short months.

I'll disagree with that assessment. I have several physical vehicles made in whole or in part with megaprims. I've had zero problems with them and even smooth sim border crossings.

Havok 4 removed most of the technical reasons for not using megaprims, physical or not. I've tested it quite a few times. What few may be left aren't likely to show up for most users and no doubt will get fixed eventually. Once the encroachment issues are solved that'll leave LL able to openly support larger prim options.

Being able to deal with overhanging objects will solve 90% of all land-related issues regardless of the types of prims involved so that's something good to have added in anyway.

A well-reasoned argument, but not supported by the facts. Our village at Lebettu makes extensive use of megaprims, and we have never had serious lag issues.

So far, I'm starting to notice the only people I've seen that speak out strongly against megas are the same people that refuse to put them into practice to find out what they actually do. (=_=)

At the same time... Some of the most impressive locations I've seen are highly reliant on megas and are practically lag/bug free, even when compared to other plain-prim builds... Actually... Especially when compared to plain prim builds. (^_^)

In fact, I've noticed they're a bit better in ways because there's less of an issue of seams and overlaps which add to the rendering cost due to unneeded polygons and 'who's in front' surface shuffling. (>_<

In all fairness to Jahar, the explanation he gives is a widely-circulated one, even though it's completely erroneous. In fact, I've heard that explanation given much more often than the correct one given by Qie - there's no surprise that it's gained its own momentum by repetition.

The reason why you hear my reasons circulated so often is that those were very serious problems under the old Havok1. Havok4 *supposedly* changed things, but I have yet to see evidence that it makes megaprims any less laggy. The initial plans for Havok4 included a limit of 256mx256mx256m for megaprims. The sole reason that Linden Labs gave for extending that limit was because of the large number of builds that used megaprims that would be adversely affected if they put it into practice.

It is true that at least under H4, I haven't seen the *massive* spikes in sim physics time and concurrent drop in time dilation that you'd get with any physical collision involving a megaprim under Havok1. However, they do still seem to have some issues with physics, and I would be very wary of using them in any situation in which physical interactions will be expected.

Finally, remember that megaprims are still NOT OFFICIALLY SUPPORTED. This is important to remember. If you build based on bugs, expect buggy behavior, 'nuff said.

The reason why you hear my reasons circulated so often is that those were very serious problems under the old Havok1. Havok4 *supposedly* changed things, but I have yet to see evidence that it makes megaprims any less laggy. The initial plans for Havok4 included a limit of 256mx256mx256m for megaprims. The sole reason that Linden Labs gave for extending that limit was because of the large number of builds that used megaprims that would be adversely affected if they put it into practice.

It is true that at least under H4, I haven't seen the *massive* spikes in sim physics time and concurrent drop in time dilation that you'd get with any physical collision involving a megaprim under Havok1. However, they do still seem to have some issues with physics, and I would be very wary of using them in any situation in which physical interactions will be expected.

Finally, remember that megaprims are still NOT OFFICIALLY SUPPORTED. This is important to remember. If you build based on bugs, expect buggy behavior, 'nuff said.

As far as making them PHYSICAL, I think I agree with you that it's a bad idea...although I've done no tests to say one way or the other for sure. As far as making them non-phantom though, I see no problems. You gotta do that, or they are useless for floors, and many other purposes.

And BTW, only once did I have a problem with our megas under Havok 1. It wasn't a sim lag issue, but a problem with a mega that insisted on being non-physical, even after it had been told not to do that.