From: Jeff King <peff@peff.net>
To: NAKAMURA Takumi <geek4civic@gmail.com>
Cc: Shawn Pearce <spearce@spearce.org>,
A Large Angry SCM <gitzilla@gmail.com>,
Sverre Rabbelier <srabbelier@gmail.com>,
git <git@vger.kernel.org>
Subject: Re: Git is not scalable with too many refs/*
Date: Mon, 13 Jun 2011 18:27:34 -0400 [thread overview]
Message-ID: <20110613222734.GD21390@sigill.intra.peff.net> (raw)
In-Reply-To: <BANLkTimEGjBMrbQpkZfWYPTZ93syiKFHdw@mail.gmail.com>
On Fri, Jun 10, 2011 at 12:59:47PM +0900, NAKAMURA Takumi wrote:
> 2011/6/10 Stephen Bash <bash@genarts.com>:
> > I've seen two different workflows develop:
> > 1) Hacking on some code in Git the programmer finds something wrong. Using Git tools he can pickaxe/bisect/etc. and find that the problem traces back to a commit imported from Subversion.
> > 2) The programmer finds something wrong, asks coworker, coworker says "see bug XYZ", bug XYZ says "Fixed in r20356".
> >
> > I agree notes is the right answer for (1), but for (2) you really want a cross reference table from Subversion rev number to Git commit.
>
> It is the point I wanted to say, thank you! I am working with svn-men.
> They often speak svn revision number. (And I have to tell them svn
> revs then)
Yeah, there is no simple way to do the bi-directional mapping in git.
If all you want are decorations on commits, notes are definitely the way
to go. They are optimized for lookup in of commit -> data. But if you
want data -> commit, the only mapping we have is refs, and they are not
well optimized for the many-refs use case.
Packed-refs are better than loose refs, but I think right now we just
load them all in to an in-memory linked list. We could load them into a
more efficient in-memory data structure, or we could perhaps even mmap
the packed-refs file and binary search it in place.
But lookup is only part of the problem. There are algorithms that want
to look at all the refs (notably fetching and pushing), which are going
to be a bit slower. We don't have a way to tell those algorithms that
those refs are uninteresting for reachability analysis, because they are
just pointing to parts of the graph that are already reachable by
regular refs. Maybe there could be a part of the refs namespace that is
ignored by "--all". I dunno. That seems like a weird inconsistency.
> FYI, I have tweaked git-rev-list for commits not to sort by date with
> --quiet. It improves git-fetch (git-rev-list --not --all) performance
> when objects is well-packed.
I'm not sure that is a good solution. Even with --quiet, we will be
walking the commit graph to find merge bases to see if things are
connected. The walking code expects date-sorting; I'm not sure what
changing that assumption will do to the code.
-Peff
next prev parent reply other threads:[~2011-06-13 22:27 UTC|newest]
Thread overview: 126+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-09 3:44 Git is not scalable with too many refs/* NAKAMURA Takumi
2011-06-09 6:50 ` Sverre Rabbelier
2011-06-09 15:23 ` Shawn Pearce
2011-06-09 15:52 ` A Large Angry SCM
2011-06-09 15:56 ` Shawn Pearce
2011-06-09 16:26 ` Jeff King
2011-06-10 3:59 ` NAKAMURA Takumi
2011-06-13 22:27 ` Jeff King [this message]
2011-06-14 0:17 ` Andreas Ericsson
2011-06-14 0:30 ` Jeff King
2011-06-14 4:41 ` Junio C Hamano
2011-06-14 7:26 ` Sverre Rabbelier
2011-06-14 10:02 ` Johan Herland
2011-06-14 10:34 ` Sverre Rabbelier
2011-06-14 17:02 ` Jeff King
2011-06-14 19:20 ` Shawn Pearce
2011-06-14 19:47 ` Jeff King
2011-06-14 20:12 ` Shawn Pearce
2011-09-08 19:53 ` Martin Fick
2011-09-09 0:52 ` Martin Fick
2011-09-09 1:05 ` Thomas Rast
2011-09-09 1:13 ` Thomas Rast
2011-09-09 15:59 ` Jens Lehmann
2011-09-25 20:43 ` Martin Fick
2011-09-26 12:41 ` Christian Couder
2011-09-26 17:47 ` Martin Fick
2011-09-26 18:56 ` Christian Couder
2011-09-30 16:41 ` Martin Fick
2011-09-30 19:26 ` Martin Fick
2011-09-30 21:02 ` Martin Fick
2011-09-30 22:06 ` Martin Fick
2011-10-01 20:41 ` Junio C Hamano
2011-10-02 5:19 ` Michael Haggerty
2011-10-03 0:46 ` Martin Fick
2011-10-04 8:08 ` Michael Haggerty
2011-10-03 18:12 ` Martin Fick
2011-10-03 19:42 ` Junio C Hamano
2011-10-04 8:16 ` Michael Haggerty
2011-10-08 20:59 ` Martin Fick
2011-10-09 5:43 ` Michael Haggerty
2011-09-28 19:38 ` Martin Fick
2011-09-28 22:10 ` Martin Fick
2011-09-29 0:54 ` Julian Phillips
2011-09-29 1:37 ` Martin Fick
2011-09-29 2:19 ` Julian Phillips
2011-09-29 16:38 ` Martin Fick
2011-09-29 18:26 ` Julian Phillips
2011-09-29 18:27 ` René Scharfe
2011-09-29 19:10 ` Junio C Hamano
2011-09-29 4:18 ` [PATCH] refs: Use binary search to lookup refs faster Julian Phillips
2011-09-29 21:57 ` Junio C Hamano
2011-09-29 22:04 ` [PATCH v2] " Julian Phillips
2011-09-29 22:06 ` [PATCH] " Junio C Hamano
2011-09-29 22:11 ` [PATCH v3] " Julian Phillips
2011-09-29 23:48 ` Junio C Hamano
2011-09-30 15:30 ` Michael Haggerty
2011-09-30 16:38 ` Junio C Hamano
2011-09-30 17:56 ` [PATCH] refs: Remove duplicates after sorting with qsort Julian Phillips
2011-10-02 5:15 ` [PATCH v3] refs: Use binary search to lookup refs faster Michael Haggerty
2011-10-02 5:45 ` Junio C Hamano
2011-10-04 20:58 ` Junio C Hamano
2011-09-30 1:13 ` Martin Fick
2011-09-30 3:44 ` Junio C Hamano
2011-09-30 8:04 ` Julian Phillips
2011-09-30 15:45 ` Martin Fick
2011-09-29 20:44 ` Git is not scalable with too many refs/* Martin Fick
2011-09-29 19:10 ` Julian Phillips
2011-09-29 20:11 ` Martin Fick
2011-09-30 9:12 ` René Scharfe
2011-09-30 16:09 ` Martin Fick
2011-09-30 16:52 ` Junio C Hamano
2011-09-30 18:17 ` René Scharfe
2011-10-01 15:28 ` René Scharfe
2011-10-01 15:38 ` [PATCH 1/8] checkout: check for "Previous HEAD" notice in t2020 René Scharfe
2011-10-01 19:02 ` Sverre Rabbelier
2011-10-01 15:43 ` [PATCH 2/8] revision: factor out add_pending_sha1 René Scharfe
2011-10-01 15:51 ` [PATCH 3/8] checkout: use add_pending_{object,sha1} in orphan check René Scharfe
2011-10-01 15:56 ` [PATCH 4/8] revision: add leak_pending flag René Scharfe
2011-10-01 16:01 ` [PATCH 5/8] bisect: use " René Scharfe
2011-10-01 16:02 ` [PATCH 6/8] bundle: " René Scharfe
2011-10-01 16:09 ` [PATCH 7/8] checkout: " René Scharfe
2011-10-01 16:16 ` [PATCH 8/8] commit: factor out clear_commit_marks_for_object_array René Scharfe
2011-09-26 15:15 ` Git is not scalable with too many refs/* Martin Fick
2011-09-26 15:21 ` Sverre Rabbelier
2011-09-26 15:48 ` Martin Fick
2011-09-26 15:56 ` Sverre Rabbelier
2011-09-26 16:38 ` Martin Fick
2011-09-26 16:49 ` Julian Phillips
2011-09-26 18:07 ` Martin Fick
2011-09-26 18:37 ` Julian Phillips
2011-09-26 20:01 ` Martin Fick
2011-09-26 20:07 ` Junio C Hamano
2011-09-26 20:28 ` Julian Phillips
2011-09-26 21:39 ` Martin Fick
2011-09-26 21:52 ` Martin Fick
2011-09-26 23:26 ` Julian Phillips
2011-09-26 23:37 ` David Michael Barr
2011-09-27 1:01 ` [PATCH] refs.c: Fix slowness with numerous loose refs David Barr
2011-09-27 2:04 ` David Michael Barr
2011-09-26 23:38 ` Git is not scalable with too many refs/* Junio C Hamano
2011-09-27 0:00 ` [PATCH] Don't sort ref_list too early Julian Phillips
2011-10-02 4:58 ` Michael Haggerty
2011-09-27 0:12 ` Git is not scalable with too many refs/* Martin Fick
2011-09-27 0:22 ` Julian Phillips
2011-09-27 2:34 ` Martin Fick
2011-09-27 7:59 ` Julian Phillips
2011-09-27 8:20 ` Sverre Rabbelier
2011-09-27 9:01 ` Julian Phillips
2011-09-27 10:01 ` Sverre Rabbelier
2011-09-27 10:25 ` Nguyen Thai Ngoc Duy
2011-09-27 11:07 ` Michael Haggerty
2011-09-27 12:10 ` Julian Phillips
2011-09-26 22:30 ` Julian Phillips
2011-09-26 15:32 ` Michael Haggerty
2011-09-26 15:42 ` Martin Fick
2011-09-26 16:25 ` Thomas Rast
2011-09-09 13:50 ` Michael Haggerty
2011-09-09 15:51 ` Michael Haggerty
2011-09-09 16:03 ` Jens Lehmann
2011-06-10 7:41 ` Andreas Ericsson
2011-06-10 19:41 ` Shawn Pearce
2011-06-10 20:12 ` Jakub Narebski
2011-06-10 20:35 ` Jeff King
2011-06-13 7:08 ` Andreas Ericsson
2011-06-09 11:18 ` Jakub Narebski
2011-06-09 15:42 ` Stephen Bash
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