From: Derrick Stolee <derrickstolee@github.com>
To: Abhradeep Chakraborty <chakrabortyabhradeep79@gmail.com>,
Johannes Schindelin <Johannes.Schindelin@gmx.de>
Cc: "Abhradeep Chakraborty via GitGitGadget" <gitgitgadget@gmail.com>,
git <git@vger.kernel.org>, "Taylor Blau" <me@ttaylorr.com>,
"Kaartic Sivaram" <kaartic.sivaraam@gmail.com>,
"Philip Oakley" <philipoakley@iee.email>,
"Martin Ågren" <martin.agren@gmail.com>
Subject: Re: [PATCH v5 3/6] pack-bitmap-write: learn pack.writeBitmapLookupTable and add tests
Date: Wed, 10 Aug 2022 13:51:27 -0400 [thread overview]
Message-ID: <805fb0df-45ab-7edd-8787-662b84201e2b@github.com> (raw)
In-Reply-To: <CAPOJW5w2NYbRkFOaqrNYVFkp5ud=aAxhGGV6gpdDPwnyx5TAVw@mail.gmail.com>
On 8/10/2022 6:04 AM, Abhradeep Chakraborty wrote:
> On Wed, Aug 10, 2022 at 2:50 PM Johannes Schindelin
> <Johannes.Schindelin@gmx.de> wrote:
>>
>> Hi Abhradeep,
>> I instrumented this, and saw that the `multi-pack-index` and
>> `multi-pack-index*.bitmap` files were unchanged by the `git repack`
>> invocation.
>
> Yeah, those two files remain unchanged here.
>
>> Re-generating the MIDX bitmap forcefully after the repack seems to fix
>> things over here:
>>
>> -- snip --
>> diff --git a/t/lib-bitmap.sh b/t/lib-bitmap.sh
>> index a95537e759b..564124bda27 100644
>> --- a/t/lib-bitmap.sh
>> +++ b/t/lib-bitmap.sh
>> @@ -438,7 +438,10 @@ midx_bitmap_partial_tests () {
>>
>> test_expect_success 'setup partial bitmaps' '
>> test_commit packed &&
>> +ls -l .git/objects/pack/ &&
>> git repack &&
>> +git multi-pack-index write --bitmap &&
>> +ls -l .git/objects/pack/ &&
>> test_commit loose &&
>> git multi-pack-index write --bitmap 2>err &&
>> test_path_is_file $midx &&
>> -- snap --
>>
>> This suggests to me that the `multi-pack-index write --bitmap 2>err` call
>> in this hunk might reuse a stale MIDX bitmap, and that _that_ might be
>> the root cause of this breakage.
>
> Yeah, the `multi-pack-index write --bitmap 2>err` is creating the
> problem. More specifically the `multi-pack-index write` part. As you
> can see in my previous comment (if you get the comment), I shared a
> screenshot there which pointed out that the multi-pack-index files in
> both cases are different. The portion from which it started to differ
> belongs to the `RIDX` chunk.
>
> So, I used some debug lines in `midx_pack_order()` function[1] and
> found that the objects are sorted differently in those cases (i.e.
> passing case and failing case). For passing case, the RIDX chunk
> contents are like below -
>
> pack_order = [ 1, 36, 11, 6, 18, 3, 19, 12, 5, 31, 27, 23, 29, 8, 38,
> 22, 9, 15, 14, 24, 37, 28, 7, 39, 10, 34, 26, 4, 30, 33, 2, 35, 17,
> 32, 0, 21, 16, 25, 13, 40, 20,]
>
> And in the failing case, this is -
>
> pack_order = [ 12, 18, 3, 19, 1, 36, 11, 6, 5, 31, 27, 23, 29, 8, 38,
> 22, 9, 15, 14, 24, 37, 28, 7, 39, 10, 34, 26, 4, 30, 33, 2, 35, 17,
> 32, 0, 21, 16, 25, 13, 40, 20,]
>
> I went further and realized that this is due to the line[2] -
>
> if (!e->preferred)
> data[i].pack |= (1U << 31);
>
> I.e. 4- 5 `pack_midx_entry` objects have different `preferred` values
> in those cases. For example,
> "46193a971f5045cb3ca6022957541f9ccddfbfe78591d8506e2d952f8113059b"
> (with pack order 12) is `preferred` in failing case (that's why it is
> in the first position) and the same is `not preferred` in the passing
> case.
>
> It may be because of reusing a stale midx bitmap (as you said). But I
> am not sure. Just to ensure myself, I compared all the other
> packfiles, idx files and a pack `.bitmap` file (which you can see
> using ls command) of failing and passing cases and found that they are
> the same.
You are right that this choice of a 'preferred' pack is part of the
root cause for this flake. This choice is not deterministic if the
mtime of some pack-files are within the same second.
I can make the flake go away with this change:
diff --git a/t/lib-bitmap.sh b/t/lib-bitmap.sh
index a95537e759b0..30347285f10f 100644
--- a/t/lib-bitmap.sh
+++ b/t/lib-bitmap.sh
@@ -438,7 +438,9 @@ midx_bitmap_partial_tests () {
test_expect_success 'setup partial bitmaps' '
test_commit packed &&
+ test_tick &&
git repack &&
+ test_tick &&
test_commit loose &&
git multi-pack-index write --bitmap 2>err &&
test_path_is_file $midx &&
However, that doesn't help us actually find out what the problem is
in our case.
I've tried exploring other considerations, resulting in this diff:
diff --git a/midx.c b/midx.c
index 9c26d04bfded..3b9094d55ae5 100644
--- a/midx.c
+++ b/midx.c
@@ -921,8 +921,9 @@ static void prepare_midx_packing_data(struct packing_data *pdata,
struct pack_midx_entry *from = &ctx->entries[ctx->pack_order[i]];
struct object_entry *to = packlist_alloc(pdata, &from->oid);
+ /* Why does removing the permutation here not change the outcome? */
oe_set_in_pack(pdata, to,
- ctx->info[ctx->pack_perm[from->pack_int_id]].p);
+ ctx->info[from->pack_int_id].p);
}
}
This method is setting up some important information, supposedly, and
in the failing case I see that the ctx->pack_perm performs a 5-cycle
( 0->1, 1->2, 2->3, 3->4, 4->0 ) but this removal does not affect _any
existing test cases_!
Turns out that the packfile sent here goes through this very trivial
path in oe_set_in_pack() every time we are writing a multi-pack-index:
static inline void oe_set_in_pack(struct packing_data *pack,
struct object_entry *e,
struct packed_git *p)
{
if (pack->in_pack_by_idx) {
if (p->index) {
e->in_pack_idx = p->index;
return;
}
/*
* We're accessing packs by index, but this pack doesn't have
* an index (e.g., because it was added since we created the
* in_pack_by_idx array). Bail to oe_map_new_pack(), which
* will convert us to using the full in_pack array, and then
* fall through to our in_pack handling.
*/
oe_map_new_pack(pack);
}
pack->in_pack[e - pack->objects] = p;
}
By debugging, I discovered we are hitting the case that calls
oe_map_new_pack(pack). The documentation for that method provides
the following (**emphasis mine**):
/*
* A new pack appears after prepare_in_pack_by_idx() has been
* run. **This is likely a race.**
*
* We could map this new pack to in_pack_by_idx[] array, but then we
* have to deal with full array anyway. And since it's hard to test
* this fall back code, just stay simple and fall back to using
* in_pack[] array.
*/
void oe_map_new_pack(struct packing_data *pack)
The issue being that prepare_packing_data() uses get_all_packs() to
get the list of pack-files, but that list is stale for some reason.
Adding a reprepare_packed_git() in advance of that call also removes
the flake (with always passing):
diff --git a/midx.c b/midx.c
index 9c26d04bfded..48db91d2728a 100644
--- a/midx.c
+++ b/midx.c
@@ -915,6 +915,7 @@ static void prepare_midx_packing_data(struct packing_data *pdata,
uint32_t i;
memset(pdata, 0, sizeof(struct packing_data));
+ reprepare_packed_git(the_repository);
prepare_packing_data(the_repository, pdata);
for (i = 0; i < ctx->entries_nr; i++) {
But this still appears like it is just a band-aid over a trickier
underlying issue.
Hopefully my rambling helps push you in a helpful direction to find
a more complete fix.
Thanks,
-Stolee
next prev parent reply other threads:[~2022-08-10 17:51 UTC|newest]
Thread overview: 162+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-20 12:33 [PATCH 0/6] [GSoC] bitmap: integrate a lookup table extension to the bitmap format Abhradeep Chakraborty via GitGitGadget
2022-06-20 12:33 ` [PATCH 1/6] Documentation/technical: describe bitmap lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-06-20 16:56 ` Derrick Stolee
2022-06-20 17:09 ` Taylor Blau
2022-06-21 8:31 ` Abhradeep Chakraborty
2022-06-22 16:26 ` Taylor Blau
2022-06-21 8:23 ` Abhradeep Chakraborty
2022-06-20 17:21 ` Taylor Blau
2022-06-21 9:22 ` Abhradeep Chakraborty
2022-06-22 16:29 ` Taylor Blau
2022-06-22 16:45 ` Abhradeep Chakraborty
2022-06-20 20:21 ` Derrick Stolee
2022-06-21 10:08 ` Abhradeep Chakraborty
2022-06-22 16:30 ` Taylor Blau
2022-06-20 12:33 ` [PATCH 2/6] pack-bitmap: prepare to read " Abhradeep Chakraborty via GitGitGadget
2022-06-20 20:49 ` Derrick Stolee
2022-06-21 10:28 ` Abhradeep Chakraborty
2022-06-20 22:06 ` Taylor Blau
2022-06-21 11:52 ` Abhradeep Chakraborty
2022-06-22 16:49 ` Taylor Blau
2022-06-22 17:18 ` Abhradeep Chakraborty
2022-06-22 21:34 ` Taylor Blau
2022-06-20 12:33 ` [PATCH 3/6] pack-bitmap-write.c: write " Abhradeep Chakraborty via GitGitGadget
2022-06-20 22:16 ` Taylor Blau
2022-06-21 12:50 ` Abhradeep Chakraborty
2022-06-22 16:51 ` Taylor Blau
2022-06-20 12:33 ` [PATCH 4/6] builtin/pack-objects.c: learn pack.writeBitmapLookupTable Taylor Blau via GitGitGadget
2022-06-20 22:18 ` Taylor Blau
2022-06-20 12:33 ` [PATCH 5/6] bitmap-commit-table: add tests for the bitmap lookup table Abhradeep Chakraborty via GitGitGadget
2022-06-22 16:54 ` Taylor Blau
2022-06-20 12:33 ` [PATCH 6/6] bitmap-lookup-table: add performance tests Abhradeep Chakraborty via GitGitGadget
2022-06-22 17:14 ` Taylor Blau
2022-06-26 13:10 ` [PATCH v2 0/6] [GSoC] bitmap: integrate a lookup table extension to the bitmap format Abhradeep Chakraborty via GitGitGadget
2022-06-26 13:10 ` [PATCH v2 1/6] Documentation/technical: describe bitmap lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-06-27 14:18 ` Derrick Stolee
2022-06-27 15:48 ` Taylor Blau
2022-06-27 16:51 ` Abhradeep Chakraborty
2022-06-26 13:10 ` [PATCH v2 2/6] pack-bitmap-write.c: write " Abhradeep Chakraborty via GitGitGadget
2022-06-27 14:35 ` Derrick Stolee
2022-06-27 16:12 ` Taylor Blau
2022-06-27 17:10 ` Abhradeep Chakraborty
2022-06-27 16:05 ` Taylor Blau
2022-06-27 18:29 ` Abhradeep Chakraborty
2022-06-26 13:10 ` [PATCH v2 3/6] pack-bitmap-write: learn pack.writeBitmapLookupTable and add tests Abhradeep Chakraborty via GitGitGadget
2022-06-27 14:43 ` Derrick Stolee
2022-06-27 17:42 ` Abhradeep Chakraborty
2022-06-27 17:49 ` Taylor Blau
2022-06-27 17:47 ` Taylor Blau
2022-06-27 18:39 ` Abhradeep Chakraborty
2022-06-29 20:11 ` Taylor Blau
2022-06-26 13:10 ` [PATCH v2 4/6] pack-bitmap: prepare to read lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-06-27 15:12 ` Derrick Stolee
2022-06-27 18:06 ` [PATCH v2 4/6] pack-bitmap: prepare to read lookup table Abhradeep Chakraborty
2022-06-27 18:32 ` Derrick Stolee
2022-06-27 21:49 ` [PATCH v2 4/6] pack-bitmap: prepare to read lookup table extension Taylor Blau
2022-06-28 8:59 ` [PATCH v2 4/6] pack-bitmap: prepare to read lookup table Abhradeep Chakraborty
2022-06-29 20:22 ` Taylor Blau
2022-06-30 6:58 ` [PATCH v2 4/6] pack-bitmap: prepare to read lookup table extension Abhradeep Chakraborty
2022-06-27 21:38 ` Taylor Blau
2022-06-28 19:25 ` Abhradeep Chakraborty
2022-06-29 20:37 ` Taylor Blau
2022-06-29 20:41 ` Taylor Blau
2022-06-30 8:35 ` Abhradeep Chakraborty
2022-06-26 13:10 ` [PATCH v2 5/6] bitmap-lookup-table: add performance tests for lookup table Abhradeep Chakraborty via GitGitGadget
2022-06-27 21:53 ` Taylor Blau
2022-06-28 7:58 ` Abhradeep Chakraborty
2022-06-29 20:40 ` Taylor Blau
2022-06-26 13:10 ` [PATCH v2 6/6] p5310-pack-bitmaps.sh: enable pack.writeReverseIndex for testing Abhradeep Chakraborty via GitGitGadget
2022-06-27 21:50 ` Taylor Blau
2022-06-28 8:01 ` Abhradeep Chakraborty
2022-07-04 8:46 ` [PATCH v3 0/6] [GSoC] bitmap: integrate a lookup table extension to the bitmap format Abhradeep Chakraborty via GitGitGadget
2022-07-04 8:46 ` [PATCH v3 1/6] Documentation/technical: describe bitmap lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-07-08 16:38 ` Philip Oakley
2022-07-09 7:53 ` Abhradeep Chakraborty
2022-07-10 15:01 ` Philip Oakley
2022-07-14 23:15 ` Taylor Blau
2022-07-15 10:36 ` Philip Oakley
2022-07-15 18:48 ` Abhradeep Chakraborty
2022-07-04 8:46 ` [PATCH v3 2/6] pack-bitmap-write.c: write " Abhradeep Chakraborty via GitGitGadget
2022-07-14 23:26 ` Taylor Blau
2022-07-15 2:22 ` Taylor Blau
2022-07-15 15:58 ` Abhradeep Chakraborty
2022-07-15 22:15 ` Taylor Blau
2022-07-16 11:50 ` Abhradeep Chakraborty
2022-07-26 0:34 ` Taylor Blau
2022-07-18 8:59 ` Martin Ågren
2022-07-04 8:46 ` [PATCH v3 3/6] pack-bitmap-write: learn pack.writeBitmapLookupTable and add tests Abhradeep Chakraborty via GitGitGadget
2022-07-04 8:46 ` [PATCH v3 4/6] pack-bitmap: prepare to read lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-07-15 2:46 ` Taylor Blau
2022-07-15 16:38 ` Abhradeep Chakraborty
2022-07-15 22:20 ` Taylor Blau
2022-07-18 9:06 ` Martin Ågren
2022-07-18 19:25 ` Abhradeep Chakraborty
2022-07-18 23:26 ` Martin Ågren
2022-07-26 0:45 ` Taylor Blau
2022-07-04 8:46 ` [PATCH v3 5/6] bitmap-lookup-table: add performance tests for lookup table Abhradeep Chakraborty via GitGitGadget
2022-07-15 2:53 ` Taylor Blau
2022-07-15 18:23 ` Abhradeep Chakraborty
2022-07-04 8:46 ` [PATCH v3 6/6] p5310-pack-bitmaps.sh: remove pack.writeReverseIndex Abhradeep Chakraborty via GitGitGadget
2022-07-04 16:35 ` [PATCH v3 0/6] [GSoC] bitmap: integrate a lookup table extension to the bitmap format Abhradeep Chakraborty
2022-07-06 19:21 ` Junio C Hamano
2022-07-07 8:48 ` Abhradeep Chakraborty
2022-07-07 18:09 ` Kaartic Sivaraam
2022-07-07 18:42 ` Abhradeep Chakraborty
2022-07-20 14:05 ` [PATCH v4 " Abhradeep Chakraborty via GitGitGadget
2022-07-20 14:05 ` [PATCH v4 1/6] Documentation/technical: describe bitmap lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-07-20 14:05 ` [PATCH v4 2/6] pack-bitmap-write.c: write " Abhradeep Chakraborty via GitGitGadget
2022-07-20 14:05 ` [PATCH v4 3/6] pack-bitmap-write: learn pack.writeBitmapLookupTable and add tests Abhradeep Chakraborty via GitGitGadget
2022-07-20 14:05 ` [PATCH v4 4/6] pack-bitmap: prepare to read lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-07-20 14:05 ` [PATCH v4 5/6] p5310-pack-bitmaps.sh: enable `pack.writeReverseIndex` Abhradeep Chakraborty via GitGitGadget
2022-07-20 14:05 ` [PATCH v4 6/6] bitmap-lookup-table: add performance tests for lookup table Abhradeep Chakraborty via GitGitGadget
2022-07-20 18:38 ` [PATCH v5 0/6] [GSoC] bitmap: integrate a lookup table extension to the bitmap format Abhradeep Chakraborty via GitGitGadget
2022-07-20 18:38 ` [PATCH v5 1/6] Documentation/technical: describe bitmap lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-07-20 18:38 ` [PATCH v5 2/6] pack-bitmap-write.c: write " Abhradeep Chakraborty via GitGitGadget
2022-07-26 0:52 ` Taylor Blau
2022-07-26 18:22 ` Abhradeep Chakraborty
2022-07-20 18:38 ` [PATCH v5 3/6] pack-bitmap-write: learn pack.writeBitmapLookupTable and add tests Abhradeep Chakraborty via GitGitGadget
2022-07-28 19:22 ` Johannes Schindelin
2022-08-02 12:40 ` Abhradeep Chakraborty
2022-08-02 15:35 ` Johannes Schindelin
2022-08-02 17:44 ` Abhradeep Chakraborty
2022-08-08 13:06 ` Johannes Schindelin
2022-08-08 13:58 ` Abhradeep Chakraborty
2022-08-09 9:03 ` Johannes Schindelin
2022-08-09 12:03 ` Abhradeep Chakraborty
2022-08-09 12:07 ` Abhradeep Chakraborty
2022-08-10 9:09 ` Johannes Schindelin
2022-08-10 9:20 ` Johannes Schindelin
2022-08-10 10:04 ` Abhradeep Chakraborty
2022-08-10 17:51 ` Derrick Stolee [this message]
2022-08-12 18:51 ` Abhradeep Chakraborty
2022-08-12 19:22 ` Derrick Stolee
2022-08-13 10:59 ` Abhradeep Chakraborty
2022-08-16 21:57 ` Taylor Blau
2022-08-17 10:02 ` Abhradeep Chakraborty
2022-08-17 20:38 ` Taylor Blau
2022-08-19 21:49 ` Taylor Blau
2022-08-13 11:05 ` Abhradeep Chakraborty
2022-08-16 18:47 ` Taylor Blau
2022-07-20 18:38 ` [PATCH v5 4/6] pack-bitmap: prepare to read lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-07-26 1:13 ` Taylor Blau
2022-07-26 18:56 ` Abhradeep Chakraborty
2022-07-26 19:36 ` Eric Sunshine
2022-07-20 18:38 ` [PATCH v5 5/6] p5310-pack-bitmaps.sh: enable `pack.writeReverseIndex` Abhradeep Chakraborty via GitGitGadget
2022-07-26 1:18 ` Taylor Blau
2022-07-26 7:15 ` Ævar Arnfjörð Bjarmason
2022-07-26 13:32 ` Derrick Stolee
2022-07-26 13:54 ` Ævar Arnfjörð Bjarmason
2022-07-26 18:17 ` Abhradeep Chakraborty
2022-07-20 18:38 ` [PATCH v5 6/6] bitmap-lookup-table: add performance tests for lookup table Abhradeep Chakraborty via GitGitGadget
2022-08-14 16:55 ` [PATCH v6 0/6] [GSoC] bitmap: integrate a lookup table extension to the bitmap format Abhradeep Chakraborty via GitGitGadget
2022-08-14 16:55 ` [PATCH v6 1/6] Documentation/technical: describe bitmap lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-08-14 16:55 ` [PATCH v6 2/6] bitmap: move `get commit positions` code to `bitmap_writer_finish` Abhradeep Chakraborty via GitGitGadget
2022-08-14 16:55 ` [PATCH v6 3/6] pack-bitmap-write.c: write lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-08-14 16:55 ` [PATCH v6 4/6] pack-bitmap-write: learn pack.writeBitmapLookupTable and add tests Abhradeep Chakraborty via GitGitGadget
2022-08-14 16:55 ` [PATCH v6 5/6] pack-bitmap: prepare to read lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-08-14 16:55 ` [PATCH v6 6/6] bitmap-lookup-table: add performance tests for lookup table Abhradeep Chakraborty via GitGitGadget
2022-08-19 21:21 ` [PATCH v6 0/6] [GSoC] bitmap: integrate a lookup table extension to the bitmap format Junio C Hamano
2022-08-22 14:42 ` Johannes Schindelin
2022-08-22 14:48 ` Taylor Blau
2022-08-25 22:16 ` Taylor Blau
2022-08-26 16:02 ` Junio C Hamano
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