Re: [Monotone-devel] Setting up a "cluster" of monotone servers

[Václav Haisman]

Richard Levitte - VMS Whacker wrote:
> Hi,
> 
> For a while, I've been thinking about what would be required to have
> more than one server respond as if they were one.  One of the goals
> with this effort is to be able to have a monotone host name (such as
> mtn.lp.se) have more than one A record (in other words, point at more
> than one server) and work seemlessly.
> 
> The problem is really two-fold:
> 
>  1. Keys, permissions and hooks.  These need to be the same on all
>     servers, or there will be trouble, either with having users
>     suddenly be presented with a different server key, and monotone
>     putting up big warnings, or with netsync rights varrying depending
>     in which server you happen to hit, or other variations depending
>     on the hooks.
>     For now, such things can be solved by having a separate set of
>     servers for administrative data, with very tight trust settings.
>     It's quite possible (I don't know yet) that the future policy
>     branches could solve the problem more or less automagically.
> 
>  2. Propagation of changes.  The way things look right now,
>     propagating changes could easily be done by having all servers
>     keep a mirror of the database and sync all changes to all the
>     other servers (or in whatever topology you desire).  The trouble
>     with this is, of course, latency.  The users may or may not
>     experience that the changes they just pushed aren't quite there,
>     that they need to push more than once if they're impatient, and so
>     on.
>     A different solution could be to make it possible for a server to
>     initiate a sync with another server, and have that done directly
>     after there's been anything happening that changes the contents of
>     the database.  This would probably just need a little bit of
>     hackery of the netsync code to have an appropriate trigger point
>     that starts the netsync, and a hook that returns a list of other
>     servers to communicate with.
> 
> Thoughts?  Ideas?  Criticism?  Is this at all possible?
> 
> Cheers,
> Richard
> 
This looks like a bad approach to solve the problem. Unless I am
mistaken, this is all because monotone locks the whole DB whenever
anybody accesses it. Well, would it not make more sense to somehow lift
this restriction instead?

--
wilx

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