The idea is to allow servers to establish a secondary network link. No messages (except PINGs) would go across the secondary link unless the primary link was broken. This is still a long way from a mesh-linked network, but might be an interesting enhancement.
We would introduce a new command for unregistered connections to server ports--SECONDARY. We would also introduce a new server<->server command with the token SC. SC would be prefixed by the introducing server and would contain the same fields as a SERVER command--lag could lead to some servers receiving the SECONDARY command before the SERVER command. We need to discuss how to represent destruction of a secondary link--is a SQUIT command enough, or must we introduce another command? We must also discuss how the fall-back is to occur--if more than one SECONDARY link has been established, how do we select which one to fall back to? My idea for this is that each link--both the primary and secondaries-- have an associated timestamp. If the primary is lost, the secondary with the oldest timestamp is promoted to the primary. I can think of three more problems that must be solved. The first is what to do with en-route messages: messages that cross with the SQUIT. The parser drops messages that are going the wrong direction. We should then remove this restriction, but that leads to potentially infinite message loops under certain types of desynchronization. The second problem is what to do with messages waiting in the sendq for the primary link--they should be resent to the secondary, but might that require re-parsing them? The third problem is what to do about certain global messages required for maintaining network synchronization--some could get lost during the transition from the primary to the secondary, but we can't simply have the server deal with multiple copies of the same change to the database. So. Discuss :) -- Kevin L. Mitchell <[EMAIL PROTECTED]>
