bzr-git, the git map, fetching revisions, and being very slow

[Russel Winder]

On Sun, 2009-11-22 at 11:32 -0600, Jelmer Vernooij wrote:
> On Sun, 2009-11-22 at 17:18 +0000, Russel Winder wrote: 
> > On Sun, 2009-11-22 at 10:57 -0600, Jelmer Vernooij wrote:
> > [ . . . ]
> > > My point was that copying data from one repository in a particular
> > > format into another repository in the same format is *always* going to
> > > be faster than copying into a different format because there would be
> > > some sort of conversion involved in the second case. It is never going
> > > to be as fast.
> > > 
> > > Perhaps we should be telling the user that an operation is expected to
> > > be slower when fetching between differing formats. 
> > 
> > I think this is a crucially important point and one that definitely
> > needs raising with the user.
> > 
> > The fact that Bazaar is hiding Subversion, Git and Mercurial
> > repositories behind Bazaar branches and the Bazaar UI is great.  The
> > fact that Bazaar is hiding Subversion, Git and Mercurial repositories
> > behind Bazaar branches and the Bazaar UI is a real pain the @rse.
> Hiding isn't the right word here, we support different repository
> formats. We're not hiding anything behind Bazaar branches - you can work
> on Git repositories with Bazaar without using any of the Bazaar formats
> in one form or another. Fetching from one git repository into another
> using Bazaar is fast, fetching from a 2a repo into another 2a repo is
> fast, fetching from a 2a repo into a 0.92 repo is slow and so is
> fetching from a git repo into a bzr repo.

I try to ensure that all my Bazaar branches and repositories use the
same format (latest stable) so I didn't think of the "different Bazaar
formats" situation.  I should have done.

I think there is an element of hiding Subversion, Git and Mercurial
repositories, since the Bazaar UI handles the backing storage without
the user having to do anything -- that is really part of the whole
point.

All of this is unified in that there should be some sort of notification
when operations between different formats are being undertaken since it
affects what the user should expect in terms of response time.  (Caveat
that there must be a silent mode operation mode with return value for
use in scripts.)

> > So being able to use Bazaar to manipulate Subversion, Git and Mercurial
> > repositories is seriously great, but it should always be clear and not
> > hidden when a non-Bazaar storage is being used.  Not only is this
> > managing user expectations, it is allowing the use transparency of
> > knowledge about the system under manipulation.
> I don't think this should be specific to foreign repositories - this
> also applies e.g. to fetches between 0.92 and 2a bzr formats.

In hindsight, yes absolutely.

So the question is:  is there a simple and clean way which is not too
intrusive of just letting the user know that a format conversion is
being undertaken so that there is extra complexity and therefore slower
response.

Let me finesse the likely complaint that Bazaar has too many formats by
saying: true, and Bazaar has to deal with the marketing of this problem,
but it is best to give the user information where the information is
needed to assess expectations of performance.


-- 
Russel.
=============================================================================
Dr Russel Winder      Partner
                                            xmpp: russel at russel.org.uk
Concertant LLP        t: +44 20 7585 2200, +44 20 7193 9203
41 Buckmaster Road,   f: +44 8700 516 084   voip: sip:russel.winder at ekiga.net
London SW11 1EN, UK   m: +44 7770 465 077   skype: russel_winder
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