launchpad-dev team mailing list archive

[Max Kanat-Alexander <mkanat@xxxxxxxxxxxxxxxxxxxx>]

On 11/19/2009 07:50 PM, Michael Hudson wrote:
>> 	So the question for this issue is--what level would you like me to
>> address it on? If you'd like me to simply work on the revision graph
>> issue, I could do that within the current architecture of loggerhead and
>> devise a fix. Probably the simplest would be to just place a mutex
>> around building a revision graph for any one branch.
> 
> That's probably a good fix for loggerhead, but maybe not sufficient for
> Launchpad.

	Okay. Well, maybe to shore up the problem a little, we could do one and
then the other. The mutex thing would be pretty quick, the scaling stuff
would be a more significant amount of time.

> Another team at Canonical tried spawning and had to give up and go back
> to paste.  So let's learn from their misfortune :)

	Fair enough. :-) It was mostly just a suggestion with no research--the
core idea being "let's scale better". :-)

> Speaking more generally, the problem is the revision cache -- can we
> make it go away, or at least handle it better?

	It would indeed seem to me like the things that loggerhead does are
largely identical to the things that normal bzr users need to do, and
that using bzrlib directly should be OK. Though perhaps on older
repository formats, less so.

> Y'see, one of the problems with a central graph store is that graphs are
> big, and any central store implies IPC which implies serialization, and
> serializing and deserializing something as big as Launchpad's revision
> graph cache is annoyingly slow.  So one idea would be to have this
> central store not serve up entire graphs, but instead be able to answer
> the questions above. 

	One would think that bzr itself should be efficient at answering those
questions, though, no? Except perhaps the merge_point_list. The stuff
needed to show RevisionLogUI, for example, is identical to what's
required to show "bzr log", yes? Similarly, RevisionUI is "bzr diff"
plus a little log info. Almost every page corresponds to a common action
taken by a normal bzr user.

> I'm not sure what the "quick patch" would be -- the mutex around
> revision graph cache building?

	Yeah.

	-Max
-- 
Max Kanat-Alexander
Chief Engineer
http://www.everythingsolved.com/
Everything Solved: Complete Computer Management