Is there an easy way to detect megaprims?

A roaming device like a TrashFinder sounds like the sort of thing that could cause a sim to crash!

Aw damn, I thought it was all resolved. =(

Yep to both of those. But both of those can happen with regular prims, too. Try alt-camming from a fully-flattened cube that's been completely top-sheared in some dimension. If you try to pull the cam from the sheared face, the cam will act like you grabbed somewhere in the next sim. And for rezzing: try rezzing against the inside of a hollow cube. For me, it works about one time in fifty, just like rezzing on a megaprim.That's very interesting that some Linden suspected warpPos teleporters; I've had relatively less trouble with those than with the simple "sit target" variety. (Not that this is in any way helpful to the problem.. just interesting.)

You know, I may be smoking crack- and I'm fully willing to accept that I am, but around the time I started this thread I removed a 100m*100m non-phantom, non-physical megaprim platform from my property. It was contained within the SE 1/4 of the sim and did not overlap sim borders, although it did cause me some confusion at one time in the past: /327/a6/216679/1.html

One of my tenants also removed some megaprims from her lot and amazingly the sim ran without failure for 8 straight days. Here's the record of restarts from the start of November until the day I posted this thread:

And here are all the restarts that happened after we cleared up the megaprims (note that there was no renter turnaround during the month of November either- it's been the same residents the whole time):

Weird. Also, is it just a coincidence that the two restarts happened at almost exactly the same time of day? I still have a ticket open with LL but they haven't found anything yet.

Fascinating.

If it was the megaprim, it seems to have only been a bad megaprim during 'prime time', looking at the failure times.

I've never seen anything quite like this in my regions, and I use megaprims all the time in dozens of them.

Did anything else change?

What we may be seeing here is interaction between something and avatars logging in at primetime, or perhaps an interaction that fails when there is maximum strain on the asset servers (prime time).

I suppose perhaps a bad collision interaction between megaprims and avatars might do it. But if this were the general case, Caledon should be constantly down hard all evening in dozens of regions, considering all the megaprims I have out and the major events we have almost nightly. We have a region go down now and then, sure, but no issues like you have had.

Were scripts reduced? I know the region I looked at *definitely* was waaaaay over the line scriptwise - something like 6000ish when even 4000 is iffy.

So far as I can tell, really nothing obvious has changed. I've been spending a lot of time in that sim too, doing some building, and performance has been fine. My tenants do seem to be a bit script-happy (some more than others), but I haven't noticed a change in script stats either way.

Seems like it should be possible to write a program using libsecondlife to check the size of every prim in a sim and report the locations of any over 10x10x10.

When we still had our island we had 2 of the 256x256 prims as a home level and a private workspace level both way up in the sky. Never in almost 2 years on the island did we have a crashing problem even after putting in the megas. Now I am also anal about scripts, texture sizes and lag as well so it might be that the sim was not even close to running at capacity.

We also used the sit TPs to move between levels. Never had a problem.

Just a FYI in case it helps

I have a question, Wildefire. Were the Megaprims at high altitude?

LOL

(And yes they were, actually, heh. But none over 512!)

I was just curious. I used to think all the tales of Mega prims being laggy were myths, but lately i have begun to wonder. I still have nothing concrete to say one way or the other though. Your experience is interesting. I noticed you said it was non-phantom. After reading Andrew Linden's technical explanation of how prim collisions are processed, I would be very hesitant to have such a large prim not set to phantom. So it very well may have played some role.

I suspect it may be a case of 'too much all at once' to some degree. I've done some wild things with otherwise empty regions - they are very hard to break. But when full...

Just a mint, sir, it's wafer thin!

*splat*


* * * * *

Here's another crazy one that is wicked hard to detect. Set your draw distance to 512m and tp into the middle sim of a large cluster.

If you think it's bad for just you, think again... grin... but people with high end machines can and will use higher draw distances as part of their normal SL experience.

I'm guessing sim-wide spikes in Images Time and Net Time, yeah?

Oh, I thought you were kidding because you and I are both champions of the "over 512 refers to size, not altitude" cause.

Well, yes and no. I am adamant that the quote was miscontrued. However That doesn't mean there may not be some truth to the falsehood. (my doesn't that sound strange )

Once Oni moves his RP sim, I should have more answers....

I heard mega prims will also eat the 1st born...so maybe a script could be written to detect that

Yeah.

This is a little hard to explain, but there is something that most servers do poorly, and that is recursive dynamic functions. Humans don't think those through very well, especially in the case of finite computing resources.

For example, for every script there has to be a bit of memory and processing time set aside to manage it. Not much, but some. This isn't the script task itself, it's the thing that knows when to bring it into existence, multithread it with everything else that is going on, and eventually remove it. And remove the managing data also, all in realtime. There are other recursive dynamic tasks, when say some process launches another, which in turn launches three more, &c &c.

It's *very* easy to start something with consequences that can't be easily forseen by the launching process - how many million nested tasks started by that one teeny little one you just started, i.e. rezzing an object that does stuff &c &c.

Now, yeah, there are traditional methods for dealing with this kind of thing. But considering that one task has to take it easy on % of time spent on process, dozens of memory concerns (textures, script space, physics, &c) - it's a really, really hard thing to do well and there is no single formula you can plug in to get it right.

So this is still just a guess, but when I see there are problems roughly corresponding to prime time I tend to doubt there is some single, easily shaken down cause.

First thing I'd do, if megaprims are suspected, is borrow an otherwise empty sim and megaprim the daylights out of it. Put in tons of them. But no other thing - just megaprims - no scripts, no high # of textures. Then take a stripped down avatar and see if you can crash the region.

Next step: load the region down with tons of scripts and see what happens when you wander in and interact a bit with the region. And so forth.

Yeah, not fun, agonising and painstaking, but that's the only real way I know to isolate what is going on, save for something even more crazy called 'whitebox testing' - a complete, step by step review of all server size code considering all data ranges and boundary conditions. Which is possibly humanly impossible at this point.

As long as they are eating those prim babies, I'm all for it ;P

Yes please. Prim babies are ghastly. Hrm, I wonder if anyone's done sculpted prim babies yet? The Uncanny Valley approacheth.

the sim would hardly crash due to a mega-prim. unless it was turned physical, but that can be detected via region/estate tools.

Heres a couple of things I've noticed when using the megaprims.

You can usually avoid the teleport interaction problems by setting your teleport target a bit higher than what is intuitive. If your coordinates when standing where you want the teleporter to end say you are at a height of 50m, set the target to 51, and you shouldn't have people teleporting inside the prim.

Rezzing objects on a megaprim seems to work a lot better if you are looking straight down at the prim instead of at a low angle. Cam around a bit and try rezzing again and you'll probably have better results. Building a new prim on a megaprim seems to always work for me. You can also create a new prim on your megaprim, then rez your objects onto that and move into place.

I've got more than a few megaprims at my place, and the only reproducable crashes I'm aware of seemed to be caused by a specific combination of avatars, or just a large number of heavily scripted avatars showing up at once.