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From: Mike Hommey <>
To: Junio C Hamano <>
Subject: Re: suboptimal behavior of fast-import in some cases with "from"
Date: Thu, 9 Jul 2015 14:52:27 +0900	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Thu, Jul 09, 2015 at 02:03:15PM +0900, Mike Hommey wrote:
> On Mon, Jul 06, 2015 at 03:54:35PM -0700, Junio C Hamano wrote:
> > Mike Hommey <> writes:
> > 
> > > One of the first things parse_from does is unconditionally throw away
> > > the tree for the given branch, and then the "from" tree is loaded. So
> > > when the "from" commit is the current head of the branch, that make
> > > fast-import do more work than necessary.
> > 
> > If it is very common that the next commit the input stream wants to
> > create is often on top of the commit that was just created, and if
> > it is very common that the input stream producer knows what the
> > commit object name of the commit that was just created, then
> > optimising for that case does not sound too bad.  It really depends
> > on two factors:
> > 
> >  - How likely is it that other people make the same mistake?
> Looks like the answer is: very. Assuming my quick glance at the code is
> not mistaken, the same mistake is made in at least (yes, the
> one that comes with git), felipec's git-remote-hg, and hg-fast-export,
> and that's 100% of the sample I looked at.
> I won't claim to know what fast-import is doing, not having looked at
> more than the parse_from* functions and the commit message for 4cabf858,
> but it seems plausible this also skips making tree deltas for those
> trees.

It doesn't /seem/ to be the case.

> >  - How bad the damage to parse_from() would be if we wanted to
> >    optimize for this case?
> I /think/ it would look like this (untested), which doesn't seem too
> damaging:

It's actually not enough. It does avoid to reread trees, but it doesn't
avoid the pack to be closed/reopened.


  reply	other threads:[~2015-07-09  5:52 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-07-06 22:07 suboptimal behavior of fast-import in some cases with "from" Mike Hommey
2015-07-06 22:54 ` Junio C Hamano
2015-07-09  5:03   ` Mike Hommey
2015-07-09  5:52     ` Mike Hommey [this message]
2015-07-09  6:50       ` [PATCH] fast-import: Do less work when given "from" matches current branch head Mike Hommey
2015-07-09 20:37         ` Junio C Hamano
2015-07-09 22:30           ` Mike Hommey
2015-07-09 22:44             ` Junio C Hamano
2015-07-09 22:47               ` Junio C Hamano

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