We have the concept of a commit notice in both the server-server and client-server protocol.
In order to optimize latency the wavesandbox wave server relays operations between clients immediately after they are validated and applied to the in-memory wavelet state on the wave server before they are persisted to disk. Later, when the operations are persisted, a follow-up commit notice is sent to inform all clients that the wavelet state is guaranteed to be persisted up to that version of the wavelet. If there is an outage anywhere in the data center, there's a risk that the wave server's in-memory state is lost, so clients can only rely on operations to "stick" once they receive a subsequent commit notice. FedOne works differently than the wavesandbox wave server because FedOne doesn't persist its state. We have decided to treat FedOne's memory as its "most persistent" wavelet state and let FedOne send a commit notice immediately when it applies operations to communicate that it has persisted them to the best of its ability. The wavesandbox web client maintains a queue of operations it has sent to the wave server which the wave server has applied but not yet committed. If an outage in a data center happens and uncommitted data on the wave server is lost then, after the service is reestablished and the client reconnects to the wave server, the client resends its queued operations and, when all goes well, the outage goes unnoticed by the user. For servers, a remote server should not persist wave state until it receives the commit notice from the hosting server. This ensures that both servers have a common view of the state of the wave. It's arguable that if you don't see a commit notice after submitting a change after a certain period of time, you should re-send the submit request. The current implementation doesn't do this yet. On Sat, Feb 20, 2010 at 17:09, antwatkins <[email protected]> wrote: > Hi, > > I am still trying to figure out the purpose of the commit-notice as it > is used within the code as part of the wavelet-update process. I was > going back over the spec and it states the commit-notice can be added > as part of the wavelet-update message. There is the private method > XmppFederationHostForDomain.waveletUpdate() that would allow this, > however, there are no public methods available that allow a wavelet- > update to be sent to a Federation Remote with the optional commit (the > public methods available allow you either to commit or send deltas, > but not both). When persistence is added as part of the wavelet- > update process, is it the intent to supply the commit-notice as part > of the update and remove the separate call in > WaveServerImpl.submitDelta()? > > Thanks, > > Anthony > > On Feb 16, 1:01 pm, Torben Weis <[email protected]> wrote: >> Hi, >> >> thanks for the code walk. This helps explaining which part of the code is >> doing this. Let's hope that Google tells us why :-) >> >> > So my question isn't much different than Torben's. Why are we sending >> > a commit-notice and what does that have to do with the fact that we >> > don't have persistence yet since the comment in >> > fedone.waveserver.WaveServerImpl.submitDelta() says: >> >> > // TODO: if persistence is added, don't send commit notice >> >> Perhaps the meaning of the comment is to send the commit notice later (i.e. >> after data has been persisted)? Currently the commit notice is sent >> automatically without waiting for any commit (just guessing). >> >> Torben >> >> >> >> > Thanks, >> >> > Anthony > > -- > 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. > > -- Anthony Baxter, [email protected] -- 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.
