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From: Jeff King <>
To: Junio C Hamano <>
Cc:, Michael Haggerty <>
Subject: Re: [PATCH v5] pack-objects mru
Date: Thu, 11 Aug 2016 12:19:03 -0400	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Thu, Aug 11, 2016 at 08:11:33AM -0700, Junio C Hamano wrote:

> Jeff King <> writes:
> > So considering "--depth" as a space-saving measure for --aggressive does
> > not seem that effective. But it feels weird to quietly drop actions
> > people might have done with previous aggressive runs.
> That argument cuts both ways, doesn't it?
> If the user explicitly asks to use lower "--depth" from the command
> line when the second repack runs, the intention is clear: the
> existing pack may use delta chains that are too long and is
> detrimental to the run-time performance, and the user wants to
> correct it by repacking with shorter delta chain.
> Should the act of letting "gc --auto" use lower "--depth", by not
> configuring to always use deeper chain, be interpreted the same way?
> I am not sure.  The old packing with large --depth is something the
> user did long time ago, and the decision the user made not to use
> large depth always is also something the user did long time ago.  I
> do not think it is so cut-and-dried which one of the two conflicting
> wishes we should honor when running the second repack, especially
> when it is run unattended like "gc --auto" does.

Good points. Explicitly saying "repack --depth=..." carries a lot more
weight to me than "git gc --auto" randomly kicking in, as far as knowing
that what the user actually wants. My patch doesn't differentiate, of
course, but I think it could.

The other problem with my patch is the fact that we don't do a good job
of finding new, in-limit deltas for the ones we discard. If you want to
do that, you really need to "git repack -f" (at least with the current
code). At which point we do not reuse the on-disk deltas at all, and the
problem is moot (you could also interpret the fact that the user did
_not_ pass "-f" as "you want to reuse deltas, which means you want to
reuse even long chains", but as you've argued above, you can make a lot
of guesses about the user's intention from what they did or did not

So if we were to go this route, I don't think my patch is quite
sufficient; we'd want something else on top to do a better job of
finding replacement deltas.

Regarding my "does not seem that effective" above, I think we should
drop the aggressive depth to 50, and I just posted a patch with
reasoning and numbers:

That's maybe orthogonal, but it does remove the weird "gc --aggressive
followed by gc --auto produces a bad pack" issue, because unless you are
doing something clever, the depth will always be 50 (modulo people who
did an aggressive pack with an older version of git :-/ ).


  reply	other threads:[~2016-08-11 16:19 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-07-29  4:04 [PATCH v2 0/7] speed up pack-objects counting with many packs Jeff King
2016-07-29  4:06 ` [PATCH v2 1/7] t/perf: add tests for many-pack scenarios Jeff King
2016-07-29  4:06 ` [PATCH v2 2/7] sha1_file: drop free_pack_by_name Jeff King
2016-07-29  4:06 ` [PATCH v2 3/7] add generic most-recently-used list Jeff King
2016-07-29  4:09 ` [PATCH v2 4/7] find_pack_entry: replace last_found_pack with MRU cache Jeff King
2016-07-29  4:10 ` [PATCH v2 5/7] pack-objects: break out of want_object loop early Jeff King
2016-07-29  4:11 ` [PATCH v2 6/7] pack-objects: compute local/ignore_pack_keep early Jeff King
2016-07-29  4:15 ` [PATCH v2 7/7] pack-objects: use mru list when iterating over packs Jeff King
2016-07-29  5:45   ` Jeff King
2016-07-29 15:02     ` Junio C Hamano
2016-08-08 14:50       ` Jeff King
2016-08-08 16:28         ` Junio C Hamano
2016-08-08 16:51           ` Jeff King
2016-08-08 17:16             ` Junio C Hamano
2016-08-09 14:04               ` Jeff King
2016-08-09 17:45                 ` Jeff King
2016-08-09 18:06                   ` Junio C Hamano
2016-08-09 22:29                 ` Junio C Hamano
2016-08-10 11:52                   ` [PATCH v3 0/2] pack-objects mru Jeff King
2016-08-10 12:02                     ` [PATCH v3 1/2] pack-objects: break delta cycles before delta-search phase Jeff King
2016-08-10 20:17                       ` Junio C Hamano
2016-08-11  5:02                         ` Jeff King
2016-08-11  5:15                           ` [PATCH v4 " Jeff King
2016-08-11  6:57                           ` [PATCH v3 " Jeff King
2016-08-11  9:20                             ` [PATCH v5] pack-objects mru Jeff King
2016-08-11  9:24                               ` [PATCH v5 1/4] provide an initializer for "struct object_info" Jeff King
2016-08-11  9:25                               ` [PATCH v5 2/4] sha1_file: make packed_object_info public Jeff King
2016-08-11  9:26                               ` [PATCH v5 3/4] pack-objects: break delta cycles before delta-search phase Jeff King
2016-08-11  9:26                               ` [PATCH v5 4/4] pack-objects: use mru list when iterating over packs Jeff King
2016-08-11  9:57                               ` [PATCH v5] pack-objects mru Jeff King
2016-08-11 15:11                                 ` Junio C Hamano
2016-08-11 16:19                                   ` Jeff King [this message]
2016-08-10 12:03                     ` [PATCH v3 2/2] pack-objects: use mru list when iterating over packs Jeff King
2016-08-10 16:47                     ` [PATCH v3 0/2] pack-objects mru Junio C Hamano
2016-08-11  4:48                       ` Jeff King

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