[Opensim-users] Are unused assets deleted?

[Ethan A. Gardener]

On Sun, Aug 12, 2018, at 11:03 AM, Haravikk wrote:
> 
> 
> > On 12 Aug 2018, at 09:52, Luisillo Contepomi <luisillocontepomi at gmail.com> wrote:
> > 
> > When you build a cube in a region and after you delete de cube will
> > remain in database forever or until you erase it manually
> > 
> > Best regards,
> > Luisillo
> 
> I don't believe this is quite true; when you create an object in a 
> region it exists only within the region where it is located, if you 
> "delete" it then it is transferred to your inventory, if you then delete 
> it from your inventory as well then it should be gone for good.

You believe, or you know?  In technical fields, the difference can mean everything.

> When you 
> rez an object in a region you are actually copying it, as each copy gets 
> its own UUID. In this sense pure objects (no contents) are nothing but 
> copies, so they only occupy space for as long as a copy exists in world, 
> or in inventory, once those are gone, the object is gone forever.

I know about copies, yes, thanks.

> 
> Where assets get tricky are things like textures, sounds, animations, 
> notecards and scripts*; these are applied to objects by GUID and fetched 
> from the asset server when needed, so even if you delete an object that 
> contains your only references to these items they don't immediately 
> disappear but instead remain on your asset server, because figuring out 
> if an asset is indeed unused at this point is difficult (it would 
> require a huge amount of extra callbacks to the asset server to keep 
> track of new/deleted references and would go out of sync if a region 
> crashes and is restored from backup).

Here I think I can see the difficulty.  I'd have to strain my brain to really understand it, though.  Maybe I'll chart it out on paper or something.  

> 
> The problem with trying to flush them out is that even if an asset is no 
> longer linked directly to an object or present in a user's inventory, it 
> is still possible for a script to reference them by GUID. Using vanilla 
> LSL for example it is possible to apply textures, trigger sounds and 
> fetch notecards using a GUID.

Um... this is where I think the OpenSim project should have taken the position, "UUIDs alone are unreliable."  In Second Life in 05/06, I remember concluding that if you want a scripted item to last, you should put everything it needs into the object itself.  My conclusion was perhaps bourne out 2 or 3 years later, when teleporters scripted to use the UUID of a TV-snow texture made by Cubey Terra were found to be blank instead.  

What about the hypergrid, will an asset keep the same UUID when transferred?

> 
> The only way to safely flush out textures, sounds and notecards (and 
> animations if you allow GUID fetching of these) would be to scour every 
> object, script and notecard on your grid for possible GUIDs, but even 
> then this is only safe if you don't allow scripts to contact external 
> services (as a user could store GUIDs in an external database for 
> example).

The relatively popular Boehm garbage collector for C and C++ can operate in exactly this way, but I'll admit that a grid database is an awful lot bigger and slower than the memory of one computer program.

> 
> This is I think why in SecondLife it costs L$10 per upload, as it stops 
> users going overboard with uploads, this is also the reason why images 
> are stored at limited sizes, sounds and animations are limited in length 
> etc.

Hmm.  The upload fee was explained as, "An economy needs sources and sinks.  The upload fee is one of the sinks."  They may have had multiple reasons, I suppose.  All the other limitations might be explained as trying to limit their bandwidth.  Textures have the additional problem of taking up memory in the graphics card, a big problem in the early '00s as graphics cards had relatively little memory couldn't decompress images on the fly.  It may still be a problem: a 2GB graphics card can be a big help, but that might be some other factor.

> 
> At the end of the day though the question is; how limited is your 
> storage really? The only cost of unused assets is in a bit of wasted 
> hard storage, but storage is pretty cheap, so unless your grid is 
> growing beyond your ability to match it then you might be trying to 
> solve a problem where the solution could be more destructive than the 
> problem itself 😏

I'm told that by the end of InWorldz, its asset server was growing by a terrabyte every month!  There's nothing "more destructive" about trying to limit that kind of growth!

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The lyf so short, the craft so long to lerne. -- Chaucer