From: Junio C Hamano <gitster@pobox.com>
To: Jeff King <peff@peff.net>
Cc: Taylor Blau <me@ttaylorr.com>,
git@vger.kernel.org, Elijah Newren <newren@gmail.com>
Subject: Re: [PATCH v2 09/23] pseudo-merge: implement support for selecting pseudo-merge commits
Date: Thu, 16 May 2024 15:43:11 -0700 [thread overview]
Message-ID: <xmqqzfspml8g.fsf@gitster.g> (raw)
In-Reply-To: <20240516080704.GA85197@coredump.intra.peff.net> (Jeff King's message of "Thu, 16 May 2024 04:07:04 -0400")
Jeff King <peff@peff.net> writes:
> motivation. Something like (assuming we're following a section on
> bitmaps in the "advanced packing" page, something I recognize also
> does not yet exist):
>
> Reachability bitmaps are most efficient when we have on-disk
> stored bitmaps for one or more of the starting points of a
> traversal. For this reason, Git prefers storing bitmaps for
> commits at the tips of refs, because traversals tend to start with
> those points.
>
> But if you have a large number of refs, it's not feasible to store
> a bitmap for _every_ ref tip. It takes up space, and just OR-ing
> all of those bitmaps together is expensive.
>
> One way we can deal with that is to create bitmaps that represent
> _groups_ of refs. When a traversal asks about the entire group,
> then we can use this single bitmap instead of considering each ref
> individually. Because these bitmaps represent the set of objects
> which would be reachable in a hypothetical merge of all of the
> commits, we call them pseudo-merge bitmaps.
Nicely put. I wish there were something like the above in the
patches when I read these patches for the first time. The concept
of "pseudo-merge" was the first hump in the road to understanding.
Eventually I figured it out, but a simple write-up like the above
would have helped readers a lot.
Thanks.
next prev parent reply other threads:[~2024-05-16 22:43 UTC|newest]
Thread overview: 157+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-20 22:04 [PATCH 00/24] pack-bitmap: pseudo-merge reachability bitmaps Taylor Blau
2024-03-20 22:05 ` [PATCH 01/24] Documentation/technical: describe pseudo-merge bitmaps format Taylor Blau
2024-03-21 21:24 ` Junio C Hamano
2024-03-21 22:13 ` Taylor Blau
2024-03-21 22:22 ` Junio C Hamano
2024-03-20 22:05 ` [PATCH 02/24] config: repo_config_get_expiry() Taylor Blau
2024-04-10 17:54 ` Jeff King
2024-04-29 19:39 ` Taylor Blau
2024-03-20 22:05 ` [PATCH 03/24] ewah: implement `ewah_bitmap_is_subset()` Taylor Blau
2024-04-10 18:05 ` Jeff King
2024-04-29 19:47 ` Taylor Blau
2024-03-20 22:05 ` [PATCH 04/24] pack-bitmap: drop unused `max_bitmaps` parameter Taylor Blau
2024-04-10 18:06 ` Jeff King
2024-03-20 22:05 ` [PATCH 05/24] pack-bitmap: move some initialization to `bitmap_writer_init()` Taylor Blau
2024-04-10 18:10 ` Jeff King
2024-03-20 22:05 ` [PATCH 06/24] pseudo-merge.ch: initial commit Taylor Blau
2024-03-20 22:05 ` [PATCH 07/24] pack-bitmap-write: support storing pseudo-merge commits Taylor Blau
2024-03-20 22:05 ` [PATCH 08/24] pack-bitmap: implement `bitmap_writer_has_bitmapped_object_id()` Taylor Blau
2024-03-20 22:05 ` [PATCH 09/24] pack-bitmap: make `bitmap_writer_push_bitmapped_commit()` public Taylor Blau
2024-03-20 22:05 ` [PATCH 10/24] pseudo-merge: implement support for selecting pseudo-merge commits Taylor Blau
2024-03-20 22:05 ` [PATCH 11/24] pack-bitmap-write.c: select " Taylor Blau
2024-03-20 22:05 ` [PATCH 12/24] pack-bitmap-write.c: write pseudo-merge table Taylor Blau
2024-03-20 22:05 ` [PATCH 13/24] pack-bitmap: extract `read_bitmap()` function Taylor Blau
2024-03-20 22:05 ` [PATCH 14/24] pseudo-merge: scaffolding for reads Taylor Blau
2024-03-20 22:05 ` [PATCH 15/24] pack-bitmap.c: read pseudo-merge extension Taylor Blau
2024-03-20 22:05 ` [PATCH 16/24] pseudo-merge: implement support for reading pseudo-merge commits Taylor Blau
2024-03-20 22:05 ` [PATCH 17/24] ewah: implement `ewah_bitmap_popcount()` Taylor Blau
2024-03-20 22:05 ` [PATCH 18/24] pack-bitmap: implement test helpers for pseudo-merge Taylor Blau
2024-03-20 22:05 ` [PATCH 19/24] t/test-lib-functions.sh: support `--date` in `test_commit_bulk()` Taylor Blau
2024-03-20 22:05 ` [PATCH 20/24] pack-bitmap.c: use pseudo-merges during traversal Taylor Blau
2024-03-20 22:06 ` [PATCH 21/24] pack-bitmap: extra trace2 information Taylor Blau
2024-03-20 22:06 ` [PATCH 22/24] ewah: `bitmap_equals_ewah()` Taylor Blau
2024-03-20 22:06 ` [PATCH 23/24] pseudo-merge: implement support for finding existing merges Taylor Blau
2024-03-20 22:06 ` [PATCH 24/24] t/perf: implement performace tests for pseudo-merge bitmaps Taylor Blau
2024-03-21 19:50 ` [PATCH 00/24] pack-bitmap: pseudo-merge reachability bitmaps Junio C Hamano
2024-04-29 20:42 ` [PATCH v2 00/23] " Taylor Blau
2024-04-29 20:42 ` [PATCH v2 01/23] Documentation/technical: describe pseudo-merge bitmaps format Taylor Blau
2024-05-06 11:52 ` Patrick Steinhardt
2024-05-06 16:37 ` Taylor Blau
2024-05-10 11:46 ` Patrick Steinhardt
2024-05-13 19:47 ` Taylor Blau
2024-05-14 6:33 ` Patrick Steinhardt
2024-04-29 20:43 ` [PATCH v2 02/23] ewah: implement `ewah_bitmap_is_subset()` Taylor Blau
2024-04-29 20:43 ` [PATCH v2 03/23] pack-bitmap: drop unused `max_bitmaps` parameter Taylor Blau
2024-04-29 20:43 ` [PATCH v2 04/23] pack-bitmap: move some initialization to `bitmap_writer_init()` Taylor Blau
2024-05-06 11:52 ` Patrick Steinhardt
2024-05-06 18:24 ` Taylor Blau
2024-04-29 20:43 ` [PATCH v2 05/23] pseudo-merge.ch: initial commit Taylor Blau
2024-04-29 20:43 ` [PATCH v2 06/23] pack-bitmap-write: support storing pseudo-merge commits Taylor Blau
2024-05-06 11:52 ` Patrick Steinhardt
2024-05-06 18:48 ` Taylor Blau
2024-05-10 11:47 ` Patrick Steinhardt
2024-05-13 18:42 ` Jeff King
2024-05-13 20:19 ` Taylor Blau
2024-04-29 20:43 ` [PATCH v2 07/23] pack-bitmap: implement `bitmap_writer_has_bitmapped_object_id()` Taylor Blau
2024-04-29 20:43 ` [PATCH v2 08/23] pack-bitmap: make `bitmap_writer_push_bitmapped_commit()` public Taylor Blau
2024-05-13 18:50 ` Jeff King
2024-05-14 0:54 ` Taylor Blau
2024-04-29 20:43 ` [PATCH v2 09/23] pseudo-merge: implement support for selecting pseudo-merge commits Taylor Blau
2024-05-06 11:53 ` Patrick Steinhardt
2024-05-06 19:58 ` Taylor Blau
2024-05-13 19:03 ` Jeff King
2024-05-14 0:58 ` Taylor Blau
2024-05-16 8:07 ` Jeff King
2024-05-16 22:43 ` Junio C Hamano [this message]
2024-04-29 20:43 ` [PATCH v2 10/23] pack-bitmap-write.c: select " Taylor Blau
2024-05-06 11:53 ` Patrick Steinhardt
2024-05-06 20:05 ` Taylor Blau
2024-05-10 11:47 ` Patrick Steinhardt
2024-04-29 20:43 ` [PATCH v2 11/23] pack-bitmap-write.c: write pseudo-merge table Taylor Blau
2024-04-29 20:43 ` [PATCH v2 12/23] pack-bitmap: extract `read_bitmap()` function Taylor Blau
2024-04-29 20:43 ` [PATCH v2 13/23] pseudo-merge: scaffolding for reads Taylor Blau
2024-04-29 20:43 ` [PATCH v2 14/23] pack-bitmap.c: read pseudo-merge extension Taylor Blau
2024-04-29 20:44 ` [PATCH v2 15/23] pseudo-merge: implement support for reading pseudo-merge commits Taylor Blau
2024-04-29 20:44 ` [PATCH v2 16/23] ewah: implement `ewah_bitmap_popcount()` Taylor Blau
2024-04-29 20:44 ` [PATCH v2 17/23] pack-bitmap: implement test helpers for pseudo-merge Taylor Blau
2024-04-29 20:44 ` [PATCH v2 18/23] t/test-lib-functions.sh: support `--date` in `test_commit_bulk()` Taylor Blau
2024-04-29 20:44 ` [PATCH v2 19/23] pack-bitmap.c: use pseudo-merges during traversal Taylor Blau
2024-04-29 20:44 ` [PATCH v2 20/23] pack-bitmap: extra trace2 information Taylor Blau
2024-04-29 20:44 ` [PATCH v2 21/23] ewah: `bitmap_equals_ewah()` Taylor Blau
2024-04-29 20:44 ` [PATCH v2 22/23] pseudo-merge: implement support for finding existing merges Taylor Blau
2024-04-29 20:44 ` [PATCH v2 23/23] t/perf: implement performace tests for pseudo-merge bitmaps Taylor Blau
2024-04-30 20:03 ` [PATCH v2 00/23] pack-bitmap: pseudo-merge reachability bitmaps Junio C Hamano
2024-05-01 14:40 ` Taylor Blau
2024-05-21 19:01 ` [PATCH v3 00/30] " Taylor Blau
2024-05-21 19:01 ` [PATCH v3 01/30] object.h: add flags allocated by pack-bitmap.h Taylor Blau
2024-05-21 19:06 ` Taylor Blau
2024-05-21 19:01 ` [PATCH v3 07/30] Documentation/gitpacking.txt: initial commit Taylor Blau
2024-05-21 19:02 ` [PATCH v3 08/30] Documentation/gitpacking.txt: describe pseudo-merge bitmaps Taylor Blau
2024-05-21 19:02 ` [PATCH v3 09/30] Documentation/technical: describe pseudo-merge bitmaps format Taylor Blau
2024-05-21 19:02 ` [PATCH v3 10/30] ewah: implement `ewah_bitmap_is_subset()` Taylor Blau
2024-05-21 19:02 ` [PATCH v3 11/30] pack-bitmap: move some initialization to `bitmap_writer_init()` Taylor Blau
2024-05-21 19:02 ` [PATCH v3 12/30] pseudo-merge.ch: initial commit Taylor Blau
2024-05-21 19:02 ` [PATCH v3 13/30] pack-bitmap-write: support storing pseudo-merge commits Taylor Blau
2024-05-21 19:02 ` [PATCH v3 14/30] pack-bitmap: implement `bitmap_writer_has_bitmapped_object_id()` Taylor Blau
2024-05-21 19:02 ` [PATCH v3 15/30] pack-bitmap: make `bitmap_writer_push_bitmapped_commit()` public Taylor Blau
2024-05-21 19:02 ` [PATCH v3 16/30] config: introduce git_config_float() Taylor Blau
2024-05-23 10:02 ` Jeff King
2024-05-23 17:51 ` Taylor Blau
2024-05-21 19:02 ` [PATCH v3 17/30] pseudo-merge: implement support for selecting pseudo-merge commits Taylor Blau
2024-05-23 10:12 ` Jeff King
2024-05-23 17:56 ` Taylor Blau
2024-05-21 19:02 ` [PATCH v3 18/30] pack-bitmap-write.c: write pseudo-merge table Taylor Blau
2024-05-21 19:02 ` [PATCH v3 19/30] pack-bitmap: extract `read_bitmap()` function Taylor Blau
2024-05-21 19:02 ` [PATCH v3 20/30] pseudo-merge: scaffolding for reads Taylor Blau
2024-05-21 19:02 ` [PATCH v3 21/30] pack-bitmap.c: read pseudo-merge extension Taylor Blau
2024-05-21 19:02 ` [PATCH v3 22/30] pseudo-merge: implement support for reading pseudo-merge commits Taylor Blau
2024-05-23 10:40 ` Jeff King
2024-05-23 18:09 ` Taylor Blau
2024-05-21 19:02 ` [PATCH v3 23/30] ewah: implement `ewah_bitmap_popcount()` Taylor Blau
2024-05-21 19:02 ` [PATCH v3 24/30] pack-bitmap: implement test helpers for pseudo-merge Taylor Blau
2024-05-21 19:02 ` [PATCH v3 25/30] t/test-lib-functions.sh: support `--date` in `test_commit_bulk()` Taylor Blau
2024-05-23 10:42 ` Jeff King
2024-05-23 15:45 ` Junio C Hamano
2024-05-23 18:23 ` Taylor Blau
2024-05-21 19:03 ` [PATCH v3 26/30] pack-bitmap.c: use pseudo-merges during traversal Taylor Blau
2024-05-23 10:48 ` Jeff King
2024-05-23 18:23 ` Taylor Blau
2024-05-21 19:03 ` [PATCH v3 27/30] pack-bitmap: extra trace2 information Taylor Blau
2024-05-21 19:03 ` [PATCH v3 28/30] ewah: `bitmap_equals_ewah()` Taylor Blau
2024-05-21 19:03 ` [PATCH v3 29/30] pseudo-merge: implement support for finding existing merges Taylor Blau
2024-05-21 19:03 ` [PATCH v3 30/30] t/perf: implement performace tests for pseudo-merge bitmaps Taylor Blau
2024-05-23 10:54 ` Jeff King
2024-05-23 19:53 ` Taylor Blau
2024-05-25 3:13 ` Jeff King
2024-05-23 11:05 ` [PATCH v3 00/30] pack-bitmap: pseudo-merge reachability bitmaps Jeff King
2024-05-23 20:04 ` Taylor Blau
2024-05-25 3:15 ` Jeff King
2024-05-23 20:42 ` Taylor Blau
2024-05-23 21:26 ` [PATCH v4 00/24] " Taylor Blau
2024-05-23 21:26 ` [PATCH v4 01/24] Documentation/gitpacking.txt: initial commit Taylor Blau
2024-05-23 21:26 ` [PATCH v4 02/24] Documentation/gitpacking.txt: describe pseudo-merge bitmaps Taylor Blau
2024-05-23 21:26 ` [PATCH v4 03/24] Documentation/technical: describe pseudo-merge bitmaps format Taylor Blau
2024-05-23 21:26 ` [PATCH v4 04/24] ewah: implement `ewah_bitmap_is_subset()` Taylor Blau
2024-05-23 21:26 ` [PATCH v4 05/24] pack-bitmap: move some initialization to `bitmap_writer_init()` Taylor Blau
2024-05-23 21:26 ` [PATCH v4 06/24] pseudo-merge.ch: initial commit Taylor Blau
2024-05-23 21:26 ` [PATCH v4 07/24] pack-bitmap-write: support storing pseudo-merge commits Taylor Blau
2024-05-23 21:26 ` [PATCH v4 08/24] pack-bitmap: implement `bitmap_writer_has_bitmapped_object_id()` Taylor Blau
2024-05-23 21:26 ` [PATCH v4 09/24] pack-bitmap: make `bitmap_writer_push_bitmapped_commit()` public Taylor Blau
2024-05-23 21:26 ` [PATCH v4 10/24] config: introduce `git_config_double()` Taylor Blau
2024-05-23 21:26 ` [PATCH v4 11/24] pseudo-merge: implement support for selecting pseudo-merge commits Taylor Blau
2024-05-25 3:22 ` Jeff King
2024-05-23 21:26 ` [PATCH v4 12/24] pack-bitmap-write.c: write pseudo-merge table Taylor Blau
2024-05-23 21:26 ` [PATCH v4 13/24] pack-bitmap: extract `read_bitmap()` function Taylor Blau
2024-05-23 21:26 ` [PATCH v4 14/24] pseudo-merge: scaffolding for reads Taylor Blau
2024-05-23 21:26 ` [PATCH v4 15/24] pack-bitmap.c: read pseudo-merge extension Taylor Blau
2024-05-23 21:26 ` [PATCH v4 16/24] pseudo-merge: implement support for reading pseudo-merge commits Taylor Blau
2024-05-23 21:27 ` [PATCH v4 17/24] ewah: implement `ewah_bitmap_popcount()` Taylor Blau
2024-05-23 21:27 ` [PATCH v4 18/24] pack-bitmap: implement test helpers for pseudo-merge Taylor Blau
2024-05-23 21:27 ` [PATCH v4 19/24] t/test-lib-functions.sh: support `--notick` in `test_commit_bulk()` Taylor Blau
2024-05-25 3:25 ` Jeff King
2024-05-23 21:27 ` [PATCH v4 20/24] pack-bitmap.c: use pseudo-merges during traversal Taylor Blau
2024-05-23 21:27 ` [PATCH v4 21/24] pack-bitmap: extra trace2 information Taylor Blau
2024-05-23 21:27 ` [PATCH v4 22/24] ewah: `bitmap_equals_ewah()` Taylor Blau
2024-05-23 21:27 ` [PATCH v4 23/24] pseudo-merge: implement support for finding existing merges Taylor Blau
2024-05-23 21:27 ` [PATCH v4 24/24] t/perf: implement performance tests for pseudo-merge bitmaps Taylor Blau
2024-05-25 3:26 ` [PATCH v4 00/24] pack-bitmap: pseudo-merge reachability bitmaps Jeff King
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