HTTP Assets Improve Grid Performance and Other Technology News 
Geschrieben von: Linden Lab   
Freitag, den 13. August 2010 um 21:28 Uhr

It been a summer of major change here at the Lab and  I wanted to give you a quick update on how we’re tackling a top  priority--platform enhancements that improve grid performance.

An Introduction to HTTP Assets
Last  week, we enabled grid-wide changes that represent an important first  step towards more effectively managing asset requests out of the  simulator path, and distributing certain assets (like textures) to an  "edge" infrastructure (like a Content Distribution Network or CDN). Internally,  the project is called HTTP Assets and includes a series of initiatives  that are intended to optimize how we manage, distribute, and store  assets on the grid to enable higher performance, reliability, and rez  times.

The HTTP Assets implementation accomplished two important objectives. The first was to move texture requests from a UDP protocol format, to TCP.  Using TCP, will increase reliability of proper receipt of those asset  requests; UDP is not designed as a reliable messaging protocol and is  used where dropping packets is preferred over the need to wait for all  packets to arrive.  The second was to reduce the need to have the  simulator directly managing asset requests. In the past, the simulator  would handle all requests from the viewer back into the inventory data  bases and asset complex, then back to the viewer. Needless to say, this  is not the most efficient or fastest way to deliver those assets to the  viewer. Now, the simulator will only be queried to provide a redirect,  so that the viewer can fetch the asset directly from a front end web  proxy to the asset system servers.  Ultimately, the simulator will be  completely removed from this path and the viewer will be querying  directly to the asset proxy server.  If you got a little lost, here’s a  visual of what the asset request process now looks like now, in two  steps:

Step 1:

Step 2:


OK, So Why Does This Matter? 
Well,  from a performance standpoint (translation - lag), you should begin to  see better texture download times. Reducing our dependency on the  simulator for these requests and eventually directing them to a services  layer will also improve the reliability of those requests.  Keep your  eyes for a blog post in a few weeks from Xan Linden, who runs the  Systems Analysis team, that will quantify those performance improvements  with hard data. He's been a Linden for a long time and is a wealth of  information on the history of our codebase and infrastructure.

One More Big Performance Improvement Now Available in Viewer 2.1
Here’s  an interesting fact. Did you know that textures and objects represent  about 90% of downloads to the Viewer? That means that any Viewer bugs  that hamper the performance of textures and objects make a big  difference when it comes to lag.

I have good news to report. We found and corrected a bug in the latest version of Viewer 2.1.  (This particular bug has been present for a while and also exists in  the 1.23 code base.) The bug was related to object retrieval, and was  causing object requests to bypass the cache and constantly make requests  for those objects to the asset system. Generally, most residents  frequent the same regions, and the objects in those regions are cached  locally so that they can be downloaded very quickly, improving overall  rez time. It’s only when objects are changed (not very frequent), or  when you visit different regions, that a request for objects are made  back to the asset system. So, download Viewer 2.1 and you should notice an appreciable improvement in performance.

More Goodness on the Horizon
Soon,  you’ll be hearing from Xan on performance data, Jack who will give us  his perspective on HTTP textures from more of a product perspective, and  also Vogt with an update from Support.

My team and I look forward to answering your questions and hearing if you feel the impact of our recent changes.


FJ Linden

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