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[Monotone-devel] Re: dumb servers

From: graydon hoare
Subject: [Monotone-devel] Re: dumb servers
Date: Sat, 17 Jan 2004 18:30:30 -0500
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Zbynek Winkler wrote:

I like the option to have a "mirror" of the my database somewhere on the server accessible to anyone at any time and when the server does not have to be smart it extends my choice of servers.

yeah, I understand this. but we've been experiencing some difficulty with the temporal log-based model of communication, so I'm considering other alternatives. if such alternatives can be made to work on "dumb" servers, all the better; but I'm more concerned with figuring out which model of communication is convergent, robust, self-stabilizing, etc. than I am insisting that the server be a pre-existing bit of internet infrastructure. if it requires a custom server, I'm willing to pay that price, if it gets us big robustness improvements.

you would have removed the these things? Suppose you have two people working on a project that are rarely online at the same time... Do you propose to sync the two databases each of them have on the workstations?

they would sync via a server or peer which *is* online all the time. that's sort of the nice thing about hashtree synchronization: it's really just set union, so if I sync with a server then you sync with the same server, you have all my changes. if I sync with the server again later, I have all your changes. it would replace probably 10 different commands in monotone with just one: "monotone sync <url>". things which reduce the amount of code so dramatically are very attractive.

While thinking more about this - depot.cgi could function as a subset of monotone knowing only how to sync databases. Is this what you meant?

I haven't made any sort of personal decision about whether to try to layer such synchronization on top of HTTP or otherwise. it's a really different model than log-replay; the only thing I am pretty sure of is that SMTP and NNTP won't fit. I'm going to experiment with using a "raw" file-descriptor based synchronization protocol between a couple experimental peer programs. if I can get that working, and get a good feeling for it being a robust algorithm, I'll look into whether we can wedge it into HTTP+CGI (or FTP/SFTP), or need to use a custom server.

I'm sorry if this all sounds like a disruptive surprise, but I've never *really* been satisfied with the networking system in monotone -- it's efficient, but a bit too fragile -- and I'd prefer to run some experiments to see if I can make it better. I promise I won't make it worse; if this stuff doesn't work in experimental runs, I won't touch any of the existing code.


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