On Fri, 18 Feb 2011 13:06:43 PST John Floren <j...@jfloren.net> wrote: > On Fri, Feb 18, 2011 at 12:15 PM, erik quanstrom <quans...@quanstro.net> wr= > ote: > >> > i don't think that it makes sense to say that since replica > >> > is slow and hg/rsync are fast, it follows that 9p is slow. > >> > >> It is the other way around. 9p can't handle latency so on > >> high latency pipes programs using 9p won't be as fast as > >> programs using streaming (instead of rpc). Granted that there > >> are many other factors when it comes to hg & replica but > >> latency is a major one. > > > > you're still comparing apples and girraffes. =A0rsync/hg have > > protocols ment for syncing. =A0replica uses 9p, which is not a > > protocol designed for syncing. =A0it's designed for regular file > > access. =A0it would be similarly difficult to use rsync's protocol > > directly for file access. > > So why does replica use 9P? Because it's *The Plan 9 Protocol*. If > *The Plan 9 Protocol* turns out to not serve our needs, we need to > figure out why.
The point I was trying to make (but clearly not clearly) was that simplicity and performance are often at cross purposes and a simple solution is not always "good enough". RPC (which is what 9p is) is simpler and perfectly fine when latencies are small but not when there is a lot of latency in relation to the amount of work doable with each rpc call. Instead of reading/writing in small chunks, you want to minimize the number of request/response round trips by conveying information at a more abstract level (which is what rsync does). > 9P as specified in the documentation might not necessarily be the > problem, but the implementation apparently is. It is inherent to 9p (and RPC). The wikipedia page on plan9 says "Plan 9 was engineered for modern distributed environments, designed from the start to be a networked operating system." -- but it _is_ curious that a networked/distributed OS does not handle latency well. This may be a heretical thing to say but there it is :-) I think it is worth looking at a successor protocol instead of just minimally fixing up 9p (a clean slate approach frees up your mind. You can then merge the two later).
