[Opensim-dev] Proposal: Implement a de-duplicating core ROBUST asset service

[Wade Schuette]

Justin,

I have to respectfully agree with Cory.

Wouldn't something like the following address your valid concerns about 
complexity and reducing total load as well as perceived system response 
time to both filing and retrieving assets?

First, if  you use event-driven processes, there's no reason to rescan 
the entire database, and by separating the processes into distinct 
streams, they are decoupled which is actually a good thing and 
simplifies both sides.   There's no reason I can see they need to be 
coupled, and separating them allows them to be optimized and tested 
separately, which is a good thing.

In fact, the entire deduplication process could run overnight at a 
low-load time, which is even better,  or have multiple "worker" 
processes assisgned to it,  if it's taking too long.   Seems very flexible.

I'm assuming that a hash-code isn't unique, but just specifies the 
bucket into which this item can be categorized.

When a new asset arrives,  if the hash-code already exists, put the 
unique-ID in a pipe and finish filing it and move on.   If the hash-code 
doesn't already exist,  just file it and move on.

At the other end of the pipe, this wakes up a process that can, as time 
allows,  check in the background to see if not only the hash-code is the 
same, but the entire item is the same, and if so,  change the handle to 
point to the existing copy.   ( For all I know,  this can be done in one 
step if CRC codes are sufficiently unique, but computing such a code is 
cpu intensive unless you can do it in hardware.)

Of course,  now the question arises of what happens when the original 
person DELETES the shared item.   If you have solid database integrity, 
you only need to know how many pointers to it exist, and if someone 
deletes "their copy",  you decrease the count by one, and when the count 
gets to one,  the next delete can actually delete the entry.



Wade




On 3/8/12 7:41 PM, Justin Clark-Casey wrote:
> On 08/03/12 22:00, Rory Slegtenhorst wrote:
>> @Justin
>> Can't we do the data de-duplication on a database level? Eg find the 
>> duplicates and just get rid of them on a regular
>> interval (cron)?
>
> This would be enormously intricate.  Not only would you have to keep 
> rescanning the entire asset db but it adds another moving part to an 
> already complex system.
>