Re: [Monotone-devel] Suspend certs...

[William Uther]

On 11/08/2007, at 4:24 PM, Thomas Keller wrote:

> William Uther schrieb:
> > >   As I threatened a while ago :), I've just merged the suspend-certs
> > > branch into trunk.  I've also used the my first real suspend  
> > > cert, in
> > > the suspend-certs branch to close off a micro-branch that I  
> > > didn't like.
> >
> > Just a quick note.  This may affect the speed of some operations.  It
> > would be good if people reported any change after the merge that  
> > affects
> > them.
> >
> > In particular, mtn ls branches is a fair bit slower now.  It would be
> > much better if it were incremental, then it wouldn't seem quite so  
> > bad.
>
> Ouch, 35.92 user against 0.06 user before.

Yeah.

The problem is that we are now running "mtn heads" on every branch to  
see if it has heads.  "mtn heads" is an inefficient operation.  (See  
project_t::get_branch_heads() in project.cc, and  
erase_ancestors_and_failures() in revision.cc if you're following  
along at home.)

To get the heads of a branch, we first get every revision that has a  
cert with that branch name.  Then we go through and erase ancestors  
and failures on that list.  This means that a full list of all  
branches requires getting every revision in the db at least once, and  
running erase ancestors on them all, one branch at a time.  This was  
discussed recently:

http://thread.gmane.org/gmane.comp.version-control.monotone.devel/11737

The impression I got from that discussion was that adding heights to  
the erase_ancestors() code wouldn't make much difference.  (I think I  
get heights now, in general.)

Some caching would be better I suspect, but you'd need to be able to  
regenerate the cache when any of the trust hooks changed.

> And somehow ls branches
> doesn't honor --ignore_suspend_certs

Um, what do you mean.  There is a test in the test-suite that  
suggests it does.  Can you provide an example?

If you mean that it doesn't speed things up again, then I agree.  I  
can patch it to look for that flag and skip some processing in that  
case.

>  (why are there underscores instead of dashes, btw?)

er, fixed.

> Can you elaborate a bit more what you mean with "incremental"?

At the moment the 'ls branches' command gathers the list of branches,  
then prints them all out.  This puts a large pause at the beginning.   
It would be better if it printed out the results as it gathered  
them.  See rev 2cd2f09be1e162f6e703cc576c11845939c552e6 for an  
example.  That revision also sends everything through lua, which I  
wasn't convinced was a good idea, so I didn't merge that with trunk.

> IMHO if
> we do not get the speed of ls branches down to only a few seconds, we
> should make --ignore_suspend_certs the default for ls branches and  
> other
>  affected commands.

Well, I think there may be some other options.  e.g. ignore trust  
hooks for 'ls branches'.  That should allow a version to be written  
that was pretty quick.

Be well,

Will         :-}