From: Taylor Blau <me@ttaylorr.com>
To: Jonathan Tan <jonathantanmy@google.com>
Cc: git@vger.kernel.org, peff@peff.net, dstolee@microsoft.com,
avarab@gmail.com, gitster@pobox.com
Subject: Re: [PATCH v2 12/15] Documentation/technical: describe multi-pack reverse indexes
Date: Tue, 2 Mar 2021 14:15:19 -0500 [thread overview]
Message-ID: <YD6OxwU936MRKa1I@nand.local> (raw)
In-Reply-To: <20210302042111.4038479-1-jonathantanmy@google.com>
On Mon, Mar 01, 2021 at 08:21:11PM -0800, Jonathan Tan wrote:
> > +== multi-pack-index reverse indexes
> > +
> > +Similar to the pack-based reverse index, the multi-pack index can also
> > +be used to generate a reverse index.
> > +
> > +Instead of mapping between offset, pack-, and index position, this
> > +reverse index maps between an object's position within the MIDX, and
> > +that object's position within a pseudo-pack that the MIDX describes.
> > +
> > +To clarify these three orderings
>
> The paragraph seems to only describe 2 orderings - object's position
> within the MIDX and object's position within the pseudo-pack. (Is the
> third one the offset within the MIDX - which is, I believe, trivially
> computable from the position within the MIDX?)
Sorry for the confusion. I was trying to distinguish between ordering
based on object offset, pack position, and index position.
I guess you could count that as 2, 3, or 4 different orderings (if you
classify "pack vs MIDX", "offset vs pack pos vs index pos" or the last
three plus "vs MIDX pos").
But I think that all of that is needlessly confusing, so I'd much rather
just say "To clarify the difference between these orderings".
> Also, which are stored in the .rev file?
The paragraph above describes it a little bit "this reverse index maps
between ...", but I think it could be made clearer. (I was intentionally
brief there since I wanted to not get too far into the details before
explaining the relevant concepts, but I think I went too far).
How does this sound?
--- >8 ---
diff --git a/Documentation/technical/pack-format.txt b/Documentation/technical/pack-format.txt
index 77eb591057..4bbbb188a4 100644
--- a/Documentation/technical/pack-format.txt
+++ b/Documentation/technical/pack-format.txt
@@ -387,12 +387,15 @@ be used to generate a reverse index.
Instead of mapping between offset, pack-, and index position, this
reverse index maps between an object's position within the MIDX, and
-that object's position within a pseudo-pack that the MIDX describes.
+that object's position within a pseudo-pack that the MIDX describes
+(i.e., the ith entry of the multi-pack reverse index holds the MIDX
+position of ith object in pseudo-pack order).
-To clarify these three orderings, consider a multi-pack reachability
-bitmap (which does not yet exist, but is what we are building towards
-here). Each bit needs to correspond to an object in the MIDX, and so we
-need an efficient mapping from bit position to MIDX position.
+To clarify the difference between these orderings, consider a multi-pack
+reachability bitmap (which does not yet exist, but is what we are
+building towards here). Each bit needs to correspond to an object in the
+MIDX, and so we need an efficient mapping from bit position to MIDX
+position.
One solution is to let bits occupy the same position in the oid-sorted
index stored by the MIDX. But because oids are effectively random, there
next prev parent reply other threads:[~2021-03-03 14:21 UTC|newest]
Thread overview: 171+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-10 23:02 [PATCH 0/9] midx: implement a multi-pack reverse index Taylor Blau
2021-02-10 23:02 ` [PATCH 1/9] t/helper/test-read-midx.c: add '--show-objects' Taylor Blau
2021-02-11 2:27 ` Derrick Stolee
2021-02-11 2:34 ` Taylor Blau
2021-02-10 23:02 ` [PATCH 2/9] midx: allow marking a pack as preferred Taylor Blau
2021-02-11 19:33 ` SZEDER Gábor
2021-02-15 15:49 ` Taylor Blau
2021-02-15 17:01 ` Ævar Arnfjörð Bjarmason
2021-02-15 18:41 ` [PATCH 0/5] commit-graph: parse_options() cleanup Ævar Arnfjörð Bjarmason
2021-02-15 18:41 ` [PATCH 1/5] commit-graph: define common usage with a macro Ævar Arnfjörð Bjarmason
2021-02-16 11:33 ` Derrick Stolee
2021-02-15 18:41 ` [PATCH 2/5] commit-graph: remove redundant handling of -h Ævar Arnfjörð Bjarmason
2021-02-16 11:35 ` Derrick Stolee
2021-02-15 18:41 ` [PATCH 3/5] commit-graph: use parse_options_concat() Ævar Arnfjörð Bjarmason
2021-02-15 18:51 ` Taylor Blau
2021-02-15 19:53 ` Taylor Blau
2021-02-15 20:39 ` Ævar Arnfjörð Bjarmason
2021-09-17 21:13 ` SZEDER Gábor
2021-09-17 22:03 ` Jeff King
2021-09-18 4:30 ` Taylor Blau
2021-09-18 7:20 ` Ævar Arnfjörð Bjarmason
2021-09-18 15:56 ` Taylor Blau
2021-09-18 15:58 ` Taylor Blau
2021-09-18 0:58 ` Ævar Arnfjörð Bjarmason
2021-02-15 18:41 ` [PATCH 4/5] commit-graph: refactor dispatch loop for style Ævar Arnfjörð Bjarmason
2021-02-15 18:53 ` Taylor Blau
2021-02-16 11:40 ` Derrick Stolee
2021-02-16 12:02 ` Ævar Arnfjörð Bjarmason
2021-02-16 18:28 ` Derrick Stolee
2021-02-15 18:41 ` [PATCH 5/5] commit-graph: show usage on "commit-graph [write|verify] garbage" Ævar Arnfjörð Bjarmason
2021-02-15 19:06 ` Taylor Blau
2021-02-16 11:43 ` Derrick Stolee
2021-02-15 21:01 ` [PATCH v2 0/4] midx: split out sub-commands Taylor Blau
2021-02-15 21:01 ` [PATCH v2 1/4] builtin/multi-pack-index.c: inline 'flags' with options Taylor Blau
2021-02-15 21:01 ` [PATCH v2 2/4] builtin/multi-pack-index.c: don't handle 'progress' separately Taylor Blau
2021-02-15 21:39 ` Ævar Arnfjörð Bjarmason
2021-02-15 21:45 ` Taylor Blau
2021-02-16 11:47 ` Derrick Stolee
2021-02-15 21:01 ` [PATCH v2 3/4] builtin/multi-pack-index.c: define common usage with a macro Taylor Blau
2021-02-15 21:01 ` [PATCH v2 4/4] builtin/multi-pack-index.c: split sub-commands Taylor Blau
2021-02-15 21:54 ` Ævar Arnfjörð Bjarmason
2021-02-15 22:34 ` Taylor Blau
2021-02-15 23:11 ` Ævar Arnfjörð Bjarmason
2021-02-15 23:49 ` Taylor Blau
2021-02-16 11:50 ` [PATCH v2 0/4] midx: split out sub-commands Derrick Stolee
2021-02-16 14:28 ` Taylor Blau
2021-02-10 23:02 ` [PATCH 3/9] midx: don't free midx_name early Taylor Blau
2021-02-10 23:02 ` [PATCH 4/9] midx: keep track of the checksum Taylor Blau
2021-02-11 2:33 ` Derrick Stolee
2021-02-11 2:35 ` Taylor Blau
2021-02-10 23:03 ` [PATCH 5/9] midx: make some functions non-static Taylor Blau
2021-02-10 23:03 ` [PATCH 6/9] Documentation/technical: describe multi-pack reverse indexes Taylor Blau
2021-02-11 2:48 ` Derrick Stolee
2021-02-11 3:03 ` Taylor Blau
2021-02-10 23:03 ` [PATCH 7/9] pack-revindex: read " Taylor Blau
2021-02-11 2:53 ` Derrick Stolee
2021-02-11 3:04 ` Taylor Blau
2021-02-11 7:54 ` Junio C Hamano
2021-02-11 14:54 ` Taylor Blau
2021-02-10 23:03 ` [PATCH 8/9] pack-write.c: extract 'write_rev_file_order' Taylor Blau
2021-02-10 23:03 ` [PATCH 9/9] pack-revindex: write multi-pack reverse indexes Taylor Blau
2021-02-11 2:58 ` [PATCH 0/9] midx: implement a multi-pack reverse index Derrick Stolee
2021-02-11 3:06 ` Taylor Blau
2021-02-11 8:13 ` Junio C Hamano
2021-02-11 18:37 ` Derrick Stolee
2021-02-11 18:55 ` Junio C Hamano
2021-02-24 19:09 ` [PATCH v2 00/15] " Taylor Blau
2021-02-24 19:09 ` [PATCH v2 01/15] builtin/multi-pack-index.c: inline 'flags' with options Taylor Blau
2021-02-24 19:09 ` [PATCH v2 02/15] builtin/multi-pack-index.c: don't handle 'progress' separately Taylor Blau
2021-02-24 19:09 ` [PATCH v2 03/15] builtin/multi-pack-index.c: define common usage with a macro Taylor Blau
2021-02-24 19:09 ` [PATCH v2 04/15] builtin/multi-pack-index.c: split sub-commands Taylor Blau
2021-03-02 4:06 ` Jonathan Tan
2021-03-02 19:02 ` Taylor Blau
2021-03-04 1:54 ` Jonathan Tan
2021-03-04 3:02 ` Taylor Blau
2021-02-24 19:09 ` [PATCH v2 05/15] builtin/multi-pack-index.c: don't enter bogus cmd_mode Taylor Blau
2021-02-24 19:09 ` [PATCH v2 06/15] builtin/multi-pack-index.c: display usage on unrecognized command Taylor Blau
2021-02-24 19:09 ` [PATCH v2 07/15] t/helper/test-read-midx.c: add '--show-objects' Taylor Blau
2021-02-24 19:09 ` [PATCH v2 08/15] midx: allow marking a pack as preferred Taylor Blau
2021-03-02 4:17 ` Jonathan Tan
2021-03-02 19:09 ` Taylor Blau
2021-03-04 2:00 ` Jonathan Tan
2021-03-04 3:04 ` Taylor Blau
2021-02-24 19:09 ` [PATCH v2 09/15] midx: don't free midx_name early Taylor Blau
2021-02-24 19:10 ` [PATCH v2 10/15] midx: keep track of the checksum Taylor Blau
2021-02-24 19:10 ` [PATCH v2 11/15] midx: make some functions non-static Taylor Blau
2021-02-24 19:10 ` [PATCH v2 12/15] Documentation/technical: describe multi-pack reverse indexes Taylor Blau
2021-03-02 4:21 ` Jonathan Tan
2021-03-02 4:36 ` Taylor Blau
2021-03-02 19:15 ` Taylor Blau [this message]
2021-03-04 2:03 ` Jonathan Tan
2021-02-24 19:10 ` [PATCH v2 13/15] pack-revindex: read " Taylor Blau
2021-03-02 18:36 ` Jonathan Tan
2021-03-03 15:27 ` Taylor Blau
2021-02-24 19:10 ` [PATCH v2 14/15] pack-write.c: extract 'write_rev_file_order' Taylor Blau
2021-02-24 19:10 ` [PATCH v2 15/15] pack-revindex: write multi-pack reverse indexes Taylor Blau
2021-03-02 18:40 ` Jonathan Tan
2021-03-03 15:30 ` Taylor Blau
2021-03-04 2:04 ` Jonathan Tan
2021-03-04 3:06 ` Taylor Blau
2021-03-11 17:04 ` [PATCH v3 00/16] midx: implement a multi-pack reverse index Taylor Blau
2021-03-11 17:04 ` [PATCH v3 01/16] builtin/multi-pack-index.c: inline 'flags' with options Taylor Blau
2021-03-29 11:20 ` Jeff King
2021-03-11 17:04 ` [PATCH v3 02/16] builtin/multi-pack-index.c: don't handle 'progress' separately Taylor Blau
2021-03-29 11:22 ` Jeff King
2021-03-11 17:04 ` [PATCH v3 03/16] builtin/multi-pack-index.c: define common usage with a macro Taylor Blau
2021-03-11 17:04 ` [PATCH v3 04/16] builtin/multi-pack-index.c: split sub-commands Taylor Blau
2021-03-29 11:36 ` Jeff King
2021-03-29 20:38 ` Taylor Blau
2021-03-30 7:04 ` Jeff King
2021-03-11 17:04 ` [PATCH v3 05/16] builtin/multi-pack-index.c: don't enter bogus cmd_mode Taylor Blau
2021-03-11 17:04 ` [PATCH v3 06/16] builtin/multi-pack-index.c: display usage on unrecognized command Taylor Blau
2021-03-29 11:42 ` Jeff King
2021-03-29 20:41 ` Taylor Blau
2021-03-11 17:05 ` [PATCH v3 07/16] t/helper/test-read-midx.c: add '--show-objects' Taylor Blau
2021-03-11 17:05 ` [PATCH v3 08/16] midx: allow marking a pack as preferred Taylor Blau
2021-03-29 12:00 ` Jeff King
2021-03-29 21:15 ` Taylor Blau
2021-03-30 7:11 ` Jeff King
2021-03-11 17:05 ` [PATCH v3 09/16] midx: don't free midx_name early Taylor Blau
2021-03-11 17:05 ` [PATCH v3 10/16] midx: keep track of the checksum Taylor Blau
2021-03-11 17:05 ` [PATCH v3 11/16] midx: make some functions non-static Taylor Blau
2021-03-11 17:05 ` [PATCH v3 12/16] Documentation/technical: describe multi-pack reverse indexes Taylor Blau
2021-03-29 12:12 ` Jeff King
2021-03-29 21:22 ` Taylor Blau
2021-03-11 17:05 ` [PATCH v3 13/16] pack-revindex: read " Taylor Blau
2021-03-29 12:43 ` Jeff King
2021-03-29 21:27 ` Taylor Blau
2021-03-11 17:05 ` [PATCH v3 14/16] pack-write.c: extract 'write_rev_file_order' Taylor Blau
2021-03-11 17:05 ` [PATCH v3 15/16] pack-revindex: write multi-pack reverse indexes Taylor Blau
2021-03-29 12:53 ` Jeff King
2021-03-29 21:30 ` Taylor Blau
2021-03-11 17:05 ` [PATCH v3 16/16] midx.c: improve cache locality in midx_pack_order_cmp() Taylor Blau
2021-03-29 12:59 ` Jeff King
2021-03-29 21:34 ` Taylor Blau
2021-03-30 7:15 ` Jeff King
2021-03-12 15:16 ` [PATCH v3 00/16] midx: implement a multi-pack reverse index Derrick Stolee
2021-03-29 13:05 ` Jeff King
2021-03-29 21:30 ` Junio C Hamano
2021-03-29 21:37 ` Taylor Blau
2021-03-30 7:15 ` Jeff King
2021-03-30 13:37 ` Taylor Blau
2021-03-30 15:03 ` [PATCH v4 " Taylor Blau
2021-03-30 15:03 ` [PATCH v4 01/16] builtin/multi-pack-index.c: inline 'flags' with options Taylor Blau
2021-03-30 15:03 ` [PATCH v4 02/16] builtin/multi-pack-index.c: don't handle 'progress' separately Taylor Blau
2021-03-30 15:03 ` [PATCH v4 03/16] builtin/multi-pack-index.c: define common usage with a macro Taylor Blau
2021-03-30 15:03 ` [PATCH v4 04/16] builtin/multi-pack-index.c: split sub-commands Taylor Blau
2021-03-30 15:04 ` [PATCH v4 05/16] builtin/multi-pack-index.c: don't enter bogus cmd_mode Taylor Blau
2021-03-30 15:04 ` [PATCH v4 06/16] builtin/multi-pack-index.c: display usage on unrecognized command Taylor Blau
2021-03-30 15:04 ` [PATCH v4 07/16] t/helper/test-read-midx.c: add '--show-objects' Taylor Blau
2021-03-30 15:04 ` [PATCH v4 08/16] midx: allow marking a pack as preferred Taylor Blau
2021-04-01 0:32 ` Taylor Blau
2021-03-30 15:04 ` [PATCH v4 09/16] midx: don't free midx_name early Taylor Blau
2021-03-30 15:04 ` [PATCH v4 10/16] midx: keep track of the checksum Taylor Blau
2021-03-30 15:04 ` [PATCH v4 11/16] midx: make some functions non-static Taylor Blau
2021-03-30 15:04 ` [PATCH v4 12/16] Documentation/technical: describe multi-pack reverse indexes Taylor Blau
2021-03-30 15:04 ` [PATCH v4 13/16] pack-revindex: read " Taylor Blau
2021-03-30 15:04 ` [PATCH v4 14/16] pack-write.c: extract 'write_rev_file_order' Taylor Blau
2021-09-08 1:08 ` [PATCH] pack-write: skip *.rev work when not writing *.rev Ævar Arnfjörð Bjarmason
2021-09-08 1:35 ` Carlo Arenas
2021-09-08 2:42 ` Taylor Blau
2021-09-08 15:47 ` Junio C Hamano
2021-09-08 2:50 ` Taylor Blau
2021-09-08 3:50 ` Taylor Blau
2021-09-08 10:18 ` Ævar Arnfjörð Bjarmason
2021-09-08 16:32 ` Taylor Blau
2021-03-30 15:04 ` [PATCH v4 15/16] pack-revindex: write multi-pack reverse indexes Taylor Blau
2021-03-30 15:04 ` [PATCH v4 16/16] midx.c: improve cache locality in midx_pack_order_cmp() Taylor Blau
2021-03-30 15:45 ` [PATCH v4 00/16] midx: implement a multi-pack reverse index Jeff King
2021-03-30 15:49 ` Taylor Blau
2021-03-30 16:01 ` Jeff King
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