Are megaprims laggy?

I hear this a lot inworld from people.

Is it a myth or a truth?

I've used a few megas here and there in builds before and not noticed anything - but maybe that's just because I don't use too many of them?

Are megas laggy? Or is the lag people see in sims with lots of megas due to something else - like sculpted mega or scripted megas?

I believe it is not so much "lag" (which can be a woefully overused/ill-defined term) as it is often issues with physics on the larger ones that cause troubles. I'm willing to be corrected on this.

As I understand it, the problem is only like to be with physical megaprims. Note that 'physical' sometimes gets confused with 'non-phantom'; I'm not aware of any problems with non-phantom megas, either.

It strikes me that in some circumstances (where a mega replaces several normal prims), they could allow quicker render times, as there are fewer polygons involved. Like Mari, I'm prepared to be corrected by techier minds.

the only problem i saw with megas was with the old gene replacment series. I find a area thatsl aggy and i look at a few floors or walls and 9times -10 its got genes instead of DayOhs or Winters.

the other thing is people seem to put HUGE textures on megas instead of repeating. one guy on a sim i was building on had a 100x50 for a wall. As its own it was ok but one day poof instant camera photo skyline and a HUGE rezz time. I asked him what he used and could i have a copy because it was so."nice" long story short after asking, it was like 2000x3000 pixels big i found out O.O
yeah. yippee. I tried pointing out going to a smaller 512x512 at least but he said it was not razor sharp and he didnt see a difference in lag to him. (he was one of those logged in 24/7 avs.)

I was just glad I didnt have to live on that sim.

you want the best megas? easily? go to xstreet and get the Salt Hud box. Its pricless! It really is.

I really can't see why there would be any difference between the old and the new batch. It's not like they carry any other information than the standard prim parameters, some of those being oversized due to a loophole.
However, there were only a few sizes in the original batch, whereas people made a *lot* of different sizes in the new batch, so it's easier to find a size which matches what you need without having to torture a prim (which adds complexity to the physics calculations).

call me crazy, ( and many have) but I have built more than a few builds that accidently had GENES in them and when done I was why the hell is it so wierdly laggy?
I look at my megas and I go DoH!
I replace the genes, lag be gone... all the proof I need to me at least. I will not use them unless absolutly needed to for some strange size.

i didn't think you could upload textures that big.

i dont think so either I think its 1024 1024.
but when he gave it to me it was 2000x3000 or so.

It will be scaled down to 1024x1024 serverside. (By fairly naive algorithms, by the way. It almost always end up looking visibly better if you do the scaling in a graphics program before uploading in a correct power-of-two size).

-Incidentally, that's why using huge textures on jewelry is a bad idea on all fronts, even if many people seem to think "The bigger the texture, the more detail my jewelry will have".
It hits you with massive lag to download big texture for something which will be a couple of pixels high on screen, and the end result will actually be visibly worse than a smaller texture scaled better.

To bring this back to the original topic, I really can't come up with any reasonable explanation/theory as to why megas should intrinsically be more laggy, even if I keep hearing anecdotal evidence.
There really shouldn't be a difference whether the math behind the prim sees a 10 or an 11.

They do potentially collide with more things, but no more than a similar area covered by several non-megas.
I have a feeling that the reason is mostly that they are easier to do stupid things with; torturing the floor avatars walk on, texturing with insanely big textures, and obviously being visible over a far bigger range, defeating the distance culling.

There may be something to these conditions as well:

Placing one against or across a region border

Having one so large (sim sized for example) that the draw distance in the viewer is faced with a choice between showing it or not showing it since its dimensions extend beyond the set LOD.

As an extension to that, and a special case of defeating distance culling, ISTR a Linden mentioning that internally handing over a prim across sim borders for viewing in a neighbouring sim is fairly expensive, and megas are, by simple virtue of their size, more prone to needing that.

So if I say... stacked 20 20m megas together and called it a building - that would have no difference in lag if I'd gone with 20 10m normals. But it might actually be less laggy than if I'd used 80 10ms?

Assuming I'm not using those old laggy ones (that's a strange finding too. Wonder what's up there.)

If I remember right, that should shrink to a 1024x1024 on upload. Unfortunately people do not know any better and use all the time when a 256x256 would do just fine.

Megaprims are always non physical so the physics engine does not come into play at all. (it might be if they WERE physical but they are not and cannot be made so)

Megaprims /might/ slow down your client some. Iv'e noticed a drop in frame rate when zoomed way in on a prim. I think most cards are optimized for tiny triangles and when the triangle take up half the screen it's actually kind of slow.

THe real bitch with megaprims is that when you are inside one (a cave or something) you can't sit on anything that doesn;t have a sit target and it makes your camera annoyingly wonky at times

Isn't that a sculpty issue and not a megaprim issue?

Actually, megaprims can be made physical. Just tick the checkbox. Or use a script (I once made a physical elevator from a 20x20x0.5; worked fine, no measurable lag as far as I could tell from sim statistics; YMMV).

Also, non-physical things still get the attention of the physics engine when, for example, computing collisions with physical objects (such as avatars clomping around on the megaprims). And a megaprim's potential collision envelope is big, so there can be a lot of such calculations.

The reason the original crop of megas could be noticeably laggier than the new ones was that the whole collection of them was generated by slicing up just a few much larger megaprims, which meant two things: the potential collision envelope was larger than it appears, and actual collisions were happening against cut faces (which apparently is harder to compute or something). It supposedly helped to make sure it was the uncut faces that were the surfaces that came in contact with avatars.

The cam and sit target things can get pretty bizarre, I quite agree. This, however, is actually much better than it used to be. Time was that you couldn't sit on anything without a sit target when inside the hollow of any prim, regardless of size, nor could you reliably rez an object on the hollow face of any prim. (For a while it would rez above the origin of a megaprim, regardless of where on the megaprim you were trying to place it.) The cam is a whole different mess, and it's still dicey to alt-zoom off the cut, sliced, hollowed, or tapered face of any prim.

Wrong.



A megaprim, turned physical. It even dropped down onto the platform when I left edit. If you have anything else to add, please check your facts before posting, or at least have the decency to admit you aren't sure.

Well aren't you just a ray of sunshine.

Ok yeah I was wrong on that one, not sure what I was thinking to tell you the truth, I actually made some giant vertical hoops and was riting the Kart around inside them, great fun

I've used quite a few megaprims on my sim at this point, replacing 75 prim landscape objects. I havent noticed any additional lag from that alone. In fact replacing 75 regular prims with one megaprim reduced the triangle count pretty massively, might actually be a benefit in that case. (Well untill I use those prims for more decoration)

I think the reason you might notice the sit target thing more with a sculpty is that the sculpty may be smaller than the bounding area of the prim originally so you end up being "inside" it even when it doesn;t look like you are. Being inside a plain megaprim definately meses wth the camera and sitting :/

i use mega's all the time..since havok 4 i haven't had really any problems with them..
the only time i can think of and it may not have even been the mega was when i cut a sphere and moved into the cut area and felt this hard lag zone..

I didn't give it much thought cause the grid was acting goofy at the time..
i have all the sets and have dipped into them all..i can't say they lag any better or worse than a regular prim..
i goofed around and made an 800+ mega prim build one time to see what would happen and
everything was fine..

i have heard though it is a good idea to stay about 10 or 15 meters away from sim borders to avoid prims drift with mega's though..

this is my 800+ mega build..pretty lag free




It was pretty big..if you look in the little corner down there you can see how small i was compared to the floor..still look like a dot in this one lol...
i think you would be fine stacking 20x20's

Not anymore.

Same with me,I had a shop once with 3 in the build and it get laggy at tp in for about 5 mins then level off.After I removed them it did not happen.so i tested it a few times that day and every time i have the megas (new ones) it be laggy when i tp in for about 5 mins.So i never use them again.Also in my sim some one had them and we all seem to be lagging out all the time.after they left and took their megas down the sim was normal.Pluss I find people that use them will defend them to the end just to justify their use.....fact is If they where so great I would think LL add them to the platform.As hard up as they seem to be to sell land these days, I would think they be offer to every one to try to sell small land parcels.

Are you talking about the gene replacment mega prims or mega prims in general?

Actually, specifically *not* the same. Ciera mentions she had problems with the old batch, but specifically *not* with the new batch. You're saying you have problems with the new batch.
This is what makes the question so hard; we cannot even get a consistent explanation of the behavior.
Also, if the lag levels off after a while, it is almost certainly a download/texture(memory) issue, not a maths issue with the shape.

As to why LL does not support them; one official (and to my knowledge so far only) explanation given is that they are just too prone to parcel encroachment and similar "social issues".
Again, that has nothing to do with the math intrinsically hitting the server hard, but with megas being too easy to (accidentally) misuse.

Back in the dark days before H4, I came upon one place that had a very strange and repeatable problem with massive sim physics lag just following scripted TPs. This turned out to be a problem with the end position of the TP landing in collision with one of the old megas. Problem completely disappeared when they changed the teleport destination slightly.

Of course, that was old physics and old megas and scripted "teleports" but I suppose something analogous *might* still be triggered under just the right conditions.

(Concur that parcel encroachment is the main--possibly the only--remaining hurdle in permitting larger-sized standard prims.)