[sldev] Unexpected objects return in group land

[Argent Stonecutter]

On 2009-07-09, at 04:23, Dale Mahalko wrote:
> On Wed, Jul 8, 2009 at 8:37 PM, Argent
> Stonecutter<secret.argent at gmail.com> wrote:
>> The correct solution (don't rez the object, leave it
>> in inventory) seems too obvious.

> This sounds like a potential race condition, since rez requests are
> not instant and load-in takes time. Assume two people want to rez
> objects on a parcel with limited space. Both attempt to rez a high
> prim object from inventory at the same time (or within milliseconds).

This is a problem that is covered in freshman CS, in the first  
database course you take.

> 1. The sim does a precheck for space availability for #1, finds enough
> room, starts the load-in
> 2. Asset system is being slow again
> 3. The sim does a precheck for space availability for #2, finds that
> another load-in is pending and not completed yet, and so aborts the
> rez attempt.
> 4. Object #`1 rezzes

That's it, the TRANSACTION-COMMIT operation every DBA is intimately  
familiar with.

With a transactionalized system, you can even allow overcommit, and  
abort (return) pending transactions when one completes. A sim in SL  
can handle up to 20,000 prims, because there ARE 20,000 prim sims in  
SL, so allowing up to 5000 prims of overcommit is acceptable.

So A says "I need 1000 prims" and it says "OK" and B says "I need 1000  
prims" and it says "OK, with 300 prims of overcommit". If be rezzes  
first, A gets returned. If you try to rez more than the buffer, then  
you get deferred. If you continue to do so, you get throttled.