Archive for June, 2009

The Costs of Free Resources

We all like it: When we get something for free!

But the non existence of costs has also disadvantages: We tend to ignore the resources that are associated with what we use. This is simply the case, because there are no costs for us, that otherwise would provide an incentive to make a more economical use of resources.

In OSGrid users like that it is possible to upload textures, animations and sound files for free. Additionally the users do not have to pay for activities like creating new groups. To make it clear: I fully back these policies, because they support the development of OSGrid.

And at this point we should all  thank the donators that cover the costs of the central infrastructure of OSGrid and that help keep it running so well every day. For sure you all know about the new “donate” button on the new Elgg based OSGrid web site.

But the missing incentives to save resources has negative effects, that over time increase the costs for central grid services unnecessarily, reduce the performance and lessen usability in certain areas.

In the following paragraphs I pick two examples to describe these issues and how these could be solved by implementing policies and tools. With this article I want to initiate a discussion about these issues, before we experience a future rapid grows of free Opensim grids.

A)  Asset Usage

People tend to upload textures, animations and sound files even if they exist within the world already. From the user point of view the costs – the time needed to check if for example a texture is available already – is higher than simply uploading it once more. Such duplicates inflate the space required for the asset database and asset caches. Additionally duplicates increase the data that needs to be transferred and thus reduces Opensim performance.

Additionally people tend to upload multiple versions of an asset to test it in world until they are happy with the result. At the end they just use the last version. Such unused assets, assets that are not referenced anymore, still consume space in the asset database that could be freed.

Possible Solution

One solution would be to introduce incentives for a more economical use of these resources. Second Life does this with their L$10 uploading fee.

But even better would be, if Opensim is able find duplicates and unused assets. Alternatively this can be done on the fly, by using some Opensim extension, or by using database scripts that are run regularly, as part of an asset database maintenance task. The goal is to remove all unreferenced assets and to replace duplicate assets with a single copy, which might include the replacement of the corresponding UUIDs.

To efficiently find duplicates, data block sizes and hash values can be used. For sure only assets that cannot be changed by individual users separately can be replaced by a single asset copy. This is especially true for uploaded textures, animations and sound files, that cannot be changed within the viewer. Notecards and scripts, that can be changed in world, and other changeable assets cannot be replaced by a single asset database copy.

In practice OSGrid uses Fragstore to do dupe compression based on 256 bit hash values for nearly 3 million assets, now. The compression achieved is about 25 percent. Currently no deletion of unused assets is done. The detection of unused assets seems to be impossible or at least very difficult with the current asset server architecture Opensim uses.

B) Creating New Groups

Groups have been introduced with Opensim revision 9215, but already today there exist nearly 600 groups in OSGrid. I have had a closer look at the existing groups and saw the following:

  • Most groups just have one member
  • There are even many groups with no members
  • Some groups have very similar names and it looks like that most of them have already been given up for newer groups with a slightly improved title

If the development continues like this, we soon will see many thousand groups, where it is difficult to identify which groups are trash and which are still used. For certain keywords group search already returns many groups with many similar names (search for “star” for example).

Possible Solution

To prevent an exaggerate use  of groups, that also reduces usability, policies and tools that support these policies should be used.

In Second Life people have to pay a fee to create a new group. Additionally the group owner has to recruit more group members within 3 days, otherwise the group gets deleted. And a group must maintain a membership of at least two members all the time in order to remain active.

In OSGrid I think we do not need a fee, but a policy for active groups similar like in Second Life. This means that empty groups and groups with less than 2 members would get deleted at latest 3 days after creation. This is the case for most groups that currently exist in OSGrid.

Additionally it might be useful to check when all group members have logged in the last time. If no group member has logged in during the last 90 days, it can be assumed, that all group members are not active OSGrid residents anymore.

A database script could check all existing groups regularly and delete groups that do not fulfill the previously mentioned conditions. For sure Opensim needs to behaves properly, if a group is encountered that was deleted and if such a group is used by land or objects shared by or deeded to that group.

In the case of shared objects and land, the group defined should simply be removed, making it unshared objects or land again. Deeded objects and land is more tricky, because in that case the group also needs to be deleted and the owner has to be reset to the previous owner before the object or land was deeded. All this should just happen if that group really was deleted. A disabled group module (maybe by accident) should not reset all group memberships.

Well, the last part was a bit technical, but it shows that implementing such a policy is something that needs to be well thought through.

Finally a little history story: As we all know, teleporting between regions also uses resources, especially processing power and bandwidth to transfer data. That is why during Second Life “stone age” they tried to introduce a fee for teleporting between regions. But understandably it did not take long, until users were demanding to abolish this teleporting fee.

I am sure that we will find a solution to prevent an exaggerate use ressources with policies and tools, without having to use money as incentive.

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Group Permissions for Land and Objects

A while ago, mcortez and his flotsam project have provided Opensim the source code to add group functionality to Opensim. And after a short interruption, because of security issues that needed to get fixed, it is now part of all newer Opensim versions and available at most OSGrid regions.

The Groups Module allows people to define and join groups. So today we all can use fancy group tags like in Second Life, which are defined as part of the group roles. In addition it is possible to send and receive group instance messages and group notices. Voice conferences can be used if all attendees are on voice enabled regions using the same voice server.

What was still missing were group permissions for land and objects. These allow land and object owners to define the rights other people have to change the contents of their parcels of land or to change objects itself.

This functionality is essential for collaborative building projects, where you want to allow just a specified group of builders to be able to rez or change objects. Till now, you had to allow all people to build on your land and to modify common objects (by tagging “allow anyone to move”). This was quite risky, because griefers could rez objects or even destroy what you have built together.

With today’s Opensim trunk version 9817 group permissions for land and objects have been added to Opensim.

To get group permissions working, I had to add group permission checks to the Opensim Permissions Module. This new functionality is very similar like in Second Life, but currently there are still limitations, because some related functionality has not been implemented in Opensim yet.

For example it is not possible to define object inventory items as being shared. And currently it is not possible to allow group members to edit certain settings of land they do not own in the About Land window. Thus currently it is not wise to deed land to a group, but land shared by a group, with the corresponding rights set in About Land, is a very useful new feature.


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