> > The TCP ACK is sufficient though. > > > > No, it's not. Just because a TCP packet has been ACK'ed does NOT mean > that > > the application has actually read the data out of the TCP recieve buffer. > > Not does it mean that the application has finished parsing the message > and > > reliably done anything with it. > > Why do you care if the application has "finished parsing the message > and reliably done anything with it?" All you do is send operations, > relying on the reliable, ordered delivery of TCP. >
And what happens when an operation gets lost between the sender and receiver? This can happen in the case where the connection is lost after the sender write the bytes to the socket, but before they where read form the socket at the other end. > > > > > 7) Distributing the OT load across multiple servers > > > > > > This already happens. Each wavelet will need to be procesed on only > one > > > > machine concurrently, but thousands of wavelets can be processed on > > > > thousands of servers concurrently. > > > > > So, by "Distributing the OT load across multiple servers" you mean > > > "putting the OT load for a given wavelet on a single server at any > > > point in time"? You still have fundamental problems - let's sat that > > > all 100,000 users all tried to edit the same wavelet. How do you > > > distribute the the OT load? You can't. You're stuffed. With TP2 in > > > the mix, you have multiple server take the load. The secret is to > > > reduce the fan-in (ie, number of connections) on each server. > > > > Frankly, I think 100,000 users all contributing to a single wavelet at > the > > same time is an extreme example > > Ok, pick a reasonable number and tell me if you think Wave is still up > to it. At what point do you think Wave will fail to scale? > The limit to scalability is the CPU power of a single machine. I suspect that wave could handle at least 1000 concurrent editors per wavelet. But I havn't done any tests to determine any actual limits. > Also, each machine will still have to process the deltas from all 100,000 > > users. Otherwise there is no way to arrive at a consistent state. > > This is true for the clients as well. each client in a 100,000 user wave, > will have > > to process the deltas from all 100,000 users. TP2 doesn't magically > reduce > > the number of transforms that will need to be applied. It just relaxes > > ordering requirements. > > > TP2 does indeed reduce the number of operations performed by each > machine. If you have a single server with 1000 connections to users > and they all happen to generate a single operation concurrently, then > the server needs to transform 1000 operations against 1000 other > operations. The naive OT algorithm is O(n^2), so 1,000,000 > transformations are required. > Actually, for the existing Wave OT, it's O(n(n+1)/2), not quite 50% of O(n^2). > If instead you use 11 servers - 10 servers each having 100 connections > to client and the final server being connected to to other 10 servers > (think of a snowflake), then each of the ten servers sees 100 > concurrent operation and performs 10,000 transformations (running > total of 100,000 operations). The final server receives 10 composite > operations (which it considers to be performed concurrently) and > transforms these composite operations against each other - that's > another 10,000 transformations. So, for the server to include all of > the operations, there was a total of 110,00 transformations - around > 10% of the single-server scenario. > > Of course, that's not the end of the story as these composite > operations get sent out to the 10 servers and all the clients. > However, no single machine ever needed to perform all of the > transformations. Downstream machines benefit from upstream > calculations, Note that different servers end up applying operations > in different orders, so TP2 must be met. > > To scale further, a system satisfying TP2 can just stick in more > servers to spread he computational load. Scaling to "100,000 users > concurrently modifying the same item" should not be a problem at all, > given enough resources. > Interesting. I hadn't considered that possibility. -Tad -- You received this message because you are subscribed to the Google Groups "Wave Protocol" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/wave-protocol?hl=en.
