From: Junio C Hamano <gitster@pobox•com>
To: Taylor Blau <me@ttaylorr•com>
Cc: git@vger•kernel.org, Elijah Newren <newren@gmail•com>,
Jeff King <peff@peff•net>, Patrick Steinhardt <ps@pks•im>
Subject: Re: [PATCH 00/11] pack-bitmap: convert offset to ref deltas where possible
Date: Thu, 10 Oct 2024 13:20:06 -0700 [thread overview]
Message-ID: <xmqq8quvk8w9.fsf@gitster.g> (raw)
In-Reply-To: <ZwgJt19kWVRTQhld@nand.local> (Taylor Blau's message of "Thu, 10 Oct 2024 13:07:03 -0400")
Taylor Blau <me@ttaylorr•com> writes:
>> So when you pick the copy of Y out of another pack, what's so
>> different? After emitting Y to the resulting pack stream (and
>> remembering where in the packstream you did so), when it is X's turn
>> to be emitted, shouldn't you be able to compute the distance in the
>> resulting packstream to represent X as an ofs-delta against Y, which
>> should already be happening when you had both X and Y in the same
>> original pack?
>
> Good question. The difference is that if you're reusing X and Y from
> same pack, you know that Y occurs some number of bytes *before* X in the
> resulting pack.
>
> But if Y comes from a different pack, it may get pushed further back in
> the MIDX pseudo-pack order. So in that case the assembled pack may list
> X before Y, in which case X cannot be an OFS_DELTA of Y, since offset
> deltas require that the base object appears first.
That is what we have always done even before we started bitmap based
optimization. If we happen to write Y before X, we consider doing
ofs-delta for X, but otherwise we do ref-delta for X. We do reorder
fairly late in the pipeline when we notice that X that we are about
to write out depends on Y that we haven't emitted to avoid this,
though. All of that the bitmap-based optimization code path should
be able to imitate, I would think.
next prev parent reply other threads:[~2024-10-10 20:20 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-10-09 20:30 [PATCH 00/11] pack-bitmap: convert offset to ref deltas where possible Taylor Blau
2024-10-09 20:31 ` [PATCH 01/11] pack-bitmap.c: do not pass `pack_pos` to `try_partial_reuse()` Taylor Blau
2024-10-09 20:31 ` [PATCH 02/11] pack-bitmap.c: avoid unnecessary `offset_to_pack_pos()` Taylor Blau
2024-10-09 20:31 ` [PATCH 03/11] pack-bitmap.c: delay calling 'offset_to_pack_pos()' Taylor Blau
2024-10-09 20:31 ` [PATCH 04/11] pack-bitmap.c: compare `base_offset` to `delta_obj_offset` Taylor Blau
2024-10-09 20:31 ` [PATCH 05/11] pack-bitmap.c: extract `find_base_bitmap_pos()` Taylor Blau
2024-10-09 20:31 ` [PATCH 06/11] pack-bitmap: drop `from_midx` field from `bitmapped_pack` Taylor Blau
2024-10-09 20:31 ` [PATCH 07/11] write_reused_pack_one(): translate bit positions directly Taylor Blau
2024-10-11 8:16 ` Jeff King
2024-11-04 20:36 ` Taylor Blau
2024-10-09 20:31 ` [PATCH 08/11] t5332: enable OFS_DELTAs via test_pack_objects_reused Taylor Blau
2024-10-11 8:19 ` Jeff King
2024-11-04 20:50 ` Taylor Blau
2024-10-09 20:31 ` [PATCH 09/11] pack-bitmap: enable cross-pack delta reuse Taylor Blau
2024-10-11 8:31 ` Jeff King
2024-11-04 21:00 ` Taylor Blau
2024-10-09 20:31 ` [PATCH 10/11] pack-bitmap.c: record whether the result was filtered Taylor Blau
2024-10-11 8:35 ` Jeff King
2024-11-04 21:01 ` Taylor Blau
2024-10-09 20:31 ` [PATCH 11/11] pack-bitmap: enable reusing deltas with base objects in 'haves' bitmap Taylor Blau
2024-10-10 16:46 ` [PATCH 00/11] pack-bitmap: convert offset to ref deltas where possible Junio C Hamano
2024-10-10 17:07 ` Taylor Blau
2024-10-10 20:20 ` Junio C Hamano [this message]
2024-10-10 20:32 ` Taylor Blau
2024-10-11 7:54 ` Jeff King
2024-10-11 8:01 ` Jeff King
2024-10-11 16:23 ` Junio C Hamano
2024-10-11 8:38 ` Jeff King
2024-11-19 23:08 ` Taylor Blau
2024-11-19 23:34 ` Taylor Blau
2024-12-18 12:57 ` Jeff King
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=xmqq8quvk8w9.fsf@gitster.g \
--to=gitster@pobox$(echo .)com \
--cc=git@vger$(echo .)kernel.org \
--cc=me@ttaylorr$(echo .)com \
--cc=newren@gmail$(echo .)com \
--cc=peff@peff$(echo .)net \
--cc=ps@pks$(echo .)im \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox