Another Bandwidth usage improvement suggestion

My suggestion is that the software should only send everything that is either dynamic or has changed from the last time I logged out, in stead of having to reload the entire universe each time that I log on.

Even though some people seems to think this is already happening, I've checked and found that it doesn't happen with me.

I have come up with two explanations:

1. Either it is resending the entire universe each time.
2. Or it resends everything each time the software version upgrades (which in my case is also every time)

Twould place undo processor strain on the server running the sim, when it tries to figure out all that has changed since you last connected. Even if you keep a snapshot of it on your computer. Which, btw, would barely be able to keep all of a few sims on there. You wouldn't be able to 'snapshot' the entire world.

Moleculor,

I believe caching an entire sim's worth of prim data would be pretty easy actually. I've written MMOG infrastructure to support a world similar to SL, and based on my understanding of SL prims, a prim object is about 230-300 bytes. Storing a full sim of prims is 3.5 - 4.5 Mbytes. That's a miniscule fraction of the 500 Meg cache I have SL set for.

Most likely they're concerned with texture caching rather than prim caching. Even a small 256x256 32bit texture is 250K. The Lindens have mentioned JPEG 2000, which gives 10:1 compression pretty easily, but that's still 25K per texture. One sim's worth of textures would be 384+ Meg.

Extrapolating from this, I would guess that SL supplies the prim updates on-demand (ie: full update when logging in, then property updates as things change), and simply passes down the texture key. If the texture key is missing in the cache, then it schedules a transfer of the texture, first at low LOD, then progressively higher.

This would lead me to believe that storing the prims is less important to the Lindeners than the management of texture data, and they have chosen to cache little, if any, of the world mesh/prims locally. Thus the need for a full download each time you log in.

I must say, streaming 3D content was genius. Now if we could get arbitrary meshes with progressive download... *sigh*

--Riptide

From what I have observed, I think it checks the modification time on objects you have in your cache by UUID. Anything that's been changed since the last time you downloaded it (determined by a simple timestamp comparison) gets resent. When I clear my cache and go to my home location, it takes some time to stream everything to me. If I log out and then in again, it's all there pretty much instantly. So it doesn't resend the full object records every time you log in, just the UUIDs.

The problem is the textures are NOT being managed well. Sending each texture LOD (or even a lower-res version before the normal higher-res version) is wasteful and inefficient. Requiring full cache redownloads on each client update is mindless. And don't get me started on the many other ways SL wastes bandwidth...

A genius SL didn't invent, incidentally. Active Worlds has been doing it since 1995. Granted, not with procedural primitive meshes, but its RWX clumps are fairly decent at being transmitted and rendering quickly.

Textures don't ever change, do they? Thus they never need to check a timestamp for a texture.

How much space would the textures on an sim occupy? I'll pick Ahern, Dore, Morris, Bonifacio, Waterhead, Help Island, and an Orientation Island as my sims of concern.

Supposedly the texture's key doesn't ever change, but the primitive's side's texture could change.

Well, if you go by Riptide's above estimate of 384MB per sim, on average, it'd be 2688MB, or 1.5+ times SL's max cache setting (which should be increasable).