From: Derrick Stolee <derrickstolee@github.com>
To: Junio C Hamano <gitster@pobox.com>,
Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com>
Cc: git@vger.kernel.org, me@ttaylorr.com, abhishekkumar8222@gmail.com
Subject: Re: [PATCH 6/7] commit-graph: parse file format v2
Date: Fri, 25 Feb 2022 08:54:08 -0500 [thread overview]
Message-ID: <a78f0808-3a58-3bab-c958-ee623b2c43fc@github.com> (raw)
In-Reply-To: <xmqq1qzrkgxg.fsf@gitster.g>
On 2/24/2022 6:01 PM, Junio C Hamano wrote:
> "Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com> writes:
>
>> From: Derrick Stolee <derrickstolee@github.com>
>>
>> The commit-graph file format v2 alters how it stores the corrected
>> commit date offsets within the Commit Data chunk instead of a separate
>> chunk. The idea is to significantly reduce the amount of data loaded
>> from disk while parsing the commit-graph.
>>
>> We need to alter the error message when we see a file format version
>> outside of our range now that multiple are possible. This has a
>> non-functional side-effect of altering a use of GRAPH_VERSION within
>> write_commit_graph().
>>
>> By storing the file format version in 'struct commit_graph', we can
>> alter the parsing code to depend on that version value. This involves
>> changing where we look for the corrected commit date offset, but also
>> which constants we use for jumping into the Generation Data Overflow
>> chunk. The Commit Data chunk only has 30 bits available for the offset
>> while the Generation Data chunk has 32 bits. This only makes a
>> meaningful difference in very malformed repositories.
>>
>> Also, we need to be careful about how we enable using corrected commit
>> dates and generation numbers to rely upon the read_generation_data value
>> instead of a non-zero value in the Commit Date chunk. In
>> generation_numbers_enabled(), the first_generation variable is
>> attemptint to look for the first topological level stored to see that it
>> is nonzero. However, for a v2 commit-graph, this value is actually
>> likely to be zero because the corrected commit date offset is probably
>> zero.
>
> I see references to OVERFLOW_V3 that comes after OVERFLOW, but there
> is no OVERFLOW_V2. Intended, or should it be V2 to match the "file
> format v2" of "generation number v2"? It is getting awkward to have
> two different version scheme ("gen v2" means corrected committer
> timestamp, whose on-disk representation is different between "file
> v1" and "file v2", and this OVERFLOW vs OVERFLOW_V3 is about the
> difference between "file v1" and "file v2" if I am following the
> series correctly).
You're right that it would be clearer to rename OVERFLOW to
OVERFLOW_V2. I'll add that to my next version when these patches
appear on their own.
Thanks,
-Stolee
next prev parent reply other threads:[~2022-02-25 13:54 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-24 20:38 [PATCH 0/7] Commit-graph: Generation Number v2 Fixes, v3 implementation Derrick Stolee via GitGitGadget
2022-02-24 20:38 ` [PATCH 1/7] test-read-graph: include extra post-parse info Derrick Stolee via GitGitGadget
2022-02-24 20:38 ` [PATCH 2/7] commit-graph: fix ordering bug in generation numbers Derrick Stolee via GitGitGadget
2022-02-24 22:15 ` Junio C Hamano
2022-02-25 13:51 ` Derrick Stolee
2022-02-25 17:35 ` Junio C Hamano
2022-02-24 20:38 ` [PATCH 3/7] commit-graph: start parsing generation v2 (again) Derrick Stolee via GitGitGadget
2022-02-28 15:18 ` Patrick Steinhardt
2022-02-28 16:23 ` Derrick Stolee
2022-02-28 16:59 ` Patrick Steinhardt
2022-02-28 18:44 ` Derrick Stolee
2022-03-01 9:46 ` Patrick Steinhardt
2022-03-01 10:35 ` Patrick Steinhardt
2022-03-01 14:06 ` Derrick Stolee
2022-03-01 14:53 ` Patrick Steinhardt
2022-03-01 15:25 ` Derrick Stolee
2022-03-02 13:57 ` Patrick Steinhardt
2022-03-02 14:57 ` Derrick Stolee
2022-03-02 18:15 ` Junio C Hamano
2022-03-02 18:46 ` Derrick Stolee
2022-03-02 22:42 ` Junio C Hamano
2022-03-03 11:19 ` Patrick Steinhardt
2022-03-03 16:00 ` Derrick Stolee
2022-03-04 14:03 ` Derrick Stolee
2022-03-07 10:34 ` Patrick Steinhardt
2022-03-07 13:45 ` Derrick Stolee
2022-03-07 17:22 ` Junio C Hamano
2022-03-10 13:58 ` Patrick Steinhardt
2022-03-10 17:18 ` Derrick Stolee
2022-02-24 20:38 ` [PATCH 4/7] commit-graph: fix generation number v2 overflow values Derrick Stolee via GitGitGadget
2022-02-24 22:35 ` Junio C Hamano
2022-02-25 13:53 ` Derrick Stolee
2022-02-25 17:38 ` Junio C Hamano
2022-02-24 20:38 ` [PATCH 5/7] commit-graph: document file format v2 Derrick Stolee via GitGitGadget
2022-02-24 22:55 ` Junio C Hamano
2022-02-25 22:31 ` Ævar Arnfjörð Bjarmason
2022-02-28 13:44 ` Derrick Stolee
2022-02-28 14:27 ` Ævar Arnfjörð Bjarmason
2022-02-28 16:39 ` Derrick Stolee
2022-02-28 21:14 ` Ævar Arnfjörð Bjarmason
2022-03-01 14:19 ` Derrick Stolee
2022-03-01 14:29 ` Ævar Arnfjörð Bjarmason
2022-03-01 15:59 ` Derrick Stolee
2022-02-24 20:38 ` [PATCH 6/7] commit-graph: parse " Derrick Stolee via GitGitGadget
2022-02-24 23:01 ` Junio C Hamano
2022-02-25 13:54 ` Derrick Stolee [this message]
2022-02-24 20:38 ` [PATCH 7/7] commit-graph: write " Derrick Stolee via GitGitGadget
2022-02-24 21:42 ` [PATCH 0/7] Commit-graph: Generation Number v2 Fixes, v3 implementation Junio C Hamano
2022-02-24 23:06 ` Junio C Hamano
2022-02-25 13:55 ` Derrick Stolee
2022-02-28 13:53 ` [PATCH v2 0/4] Commit-graph: Generation Number v2 Fixes Derrick Stolee via GitGitGadget
2022-02-28 13:53 ` [PATCH v2 1/4] test-read-graph: include extra post-parse info Derrick Stolee via GitGitGadget
2022-02-28 15:22 ` Ævar Arnfjörð Bjarmason
2022-02-28 13:53 ` [PATCH v2 2/4] commit-graph: fix ordering bug in generation numbers Derrick Stolee via GitGitGadget
2022-02-28 15:25 ` Ævar Arnfjörð Bjarmason
2022-02-28 13:53 ` [PATCH v2 3/4] commit-graph: start parsing generation v2 (again) Derrick Stolee via GitGitGadget
2022-02-28 15:30 ` Ævar Arnfjörð Bjarmason
2022-02-28 16:43 ` Derrick Stolee
2022-02-28 13:53 ` [PATCH v2 4/4] commit-graph: fix generation number v2 overflow values Derrick Stolee via GitGitGadget
2022-02-28 15:40 ` Ævar Arnfjörð Bjarmason
2022-03-01 17:23 ` [PATCH v2 0/4] Commit-graph: Generation Number v2 Fixes Ævar Arnfjörð Bjarmason
2022-03-01 19:48 ` [PATCH v3 0/5] " Derrick Stolee via GitGitGadget
2022-03-01 19:48 ` [PATCH v3 1/5] test-read-graph: include extra post-parse info Derrick Stolee via GitGitGadget
2022-03-01 19:48 ` [PATCH v3 2/5] t5318: extract helpers to lib-commit-graph.sh Derrick Stolee via GitGitGadget
2022-03-01 19:48 ` [PATCH v3 3/5] commit-graph: fix ordering bug in generation numbers Derrick Stolee via GitGitGadget
2022-03-01 20:13 ` Junio C Hamano
2022-03-01 20:30 ` Junio C Hamano
2022-03-02 14:13 ` Derrick Stolee
2022-03-01 19:48 ` [PATCH v3 4/5] commit-graph: start parsing generation v2 (again) Derrick Stolee via GitGitGadget
2022-03-01 19:48 ` [PATCH v3 5/5] commit-graph: fix generation number v2 overflow values Derrick Stolee via GitGitGadget
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