On 09.10.2020 18:49, Derrick Stolee wrote:
> On 10/9/2020 11:29 AM, Thomas Braun wrote:
>> I think I have a starting point for what goes wrong. I found a local
>> repo with another broken commit graph. And after some fiddling the
>> following script can reproduce it. I tried with git/git first but that
>> seems not to trigger that.
> 
> I'm glad you're able to trigger bad commit-graph data somehow.
> Let's see what's going on:
> 
>> # rm -rf dummy
>> mkdir dummy
>> cd dummy
>>
>> git init
>>
>> git remote add origin https://github.com/tango-controls/cppTango
>> git remote add fork1 https://github.com/bourtemb/cppTango
>> git remote add fork2 https://github.com/t-b/cppTango
>> git fetch --all --jobs 12
> 
> My gut reaction is that this parallel fetching is causing
> an issue, but we will see. Do you get a repro if you drop
> the "--jobs 12"?
> 
>> git commit-graph verify
>> rm -rf .git/objects/info/commit-graphs/
>> git commit-graph verify
>> git fetch --jobs 12
>> git remote add fork3 git@github.com:t-b/cppTango.git
>> git commit-graph verify
>> git remote add fork4 git@github.com:t-b/cppTango.git
>> git fetch --jobs 12
>> git commit-graph verify
>>
>> The last verify outputs
>>
>> commit-graph generation for commit
>> 029341567c24582030592585b395f4438273263f is 1054 != 1
>> commit-graph generation for commit
>> 1e8d10aec7ca6075f622c447d416071390698124 is 4294967295 != 1171
>> commit-graph generation for commit
>> 296e93516189c0134843fd56ac4f10d36ccf284f is 1054 != 1
>> commit-graph generation for commit
>> 4c0a7a3cd369d06b99d867be6b47a96c519efd7f is 1054 != 1
>> commit-graph has non-zero generation number for commit
>> 4d39849950d3dc02b7426c780ac7991ec7221176, but zero elsewhere
>> commit-graph has non-zero generation number for commit 4
>> [....]
> 
> This looks more troubling than just duplicate rows, but
> perhaps those duplicate rows are causing sufficient
> confusion when reading the commit-graph during the
> 'verify' command?
> 
> I tried incorporating this into the Git test suite so I
> could test it on v2.29.0-rc0 and the current merge-check,
> but I'm failing to reproduce the failure with this script:
> 
> diff --git a/t/t5324-split-commit-graph.sh b/t/t5324-split-commit-graph.sh
> index c334ee9155..2b3f3db593 100755
> --- a/t/t5324-split-commit-graph.sh
> +++ b/t/t5324-split-commit-graph.sh
> @@ -440,4 +440,26 @@ test_expect_success '--split=replace with partial Bloom data' '
>  	verify_chain_files_exist $graphdir
>  '
>  
> +test_expect_success 'test' '
> +	git init dummy &&
> +	(
> +		cd dummy &&
> +		export GIT_TRACE2_EVENT="$TRASH_DIRECTORY/../trace.txt" &&
> +		git config fetch.writeCommitGraph true &&
> +		git remote add origin https://github.com/tango-controls/cppTango &&
> +		git remote add fork1 https://github.com/bourtemb/cppTango &&
> +		git remote add fork2 https://github.com/t-b/cppTango &&
> +		git fetch --all --jobs 12 &&
> +		git commit-graph verify &&
> +		rm -rf .git/objects/info/commit-graphs/ &&
> +		git commit-graph verify &&
> +		git fetch --jobs 12 &&
> +		git remote add fork3 git@github.com:t-b/cppTango.git &&
> +		git commit-graph verify &&
> +		git remote add fork4 git@github.com:t-b/cppTango.git &&
> +		git fetch --jobs 12 &&
> +		git commit-graph verify
> +	)
> +'
> +
>  test_done
> 
> I tried this on Linux and Windows, and under "--stress" but never
> saw a failure.
> 
> Thomas: some things that could possibly help is if you repro this
> situation but also do something like
> 
> 	export GIT_TRACE2_EVENT="$(pwd)/trace.txt"
> 
> so we can read the details of everything Git is tracing during
> these parallel jobs. We might be able to stitch together a
> sequence of events that lead to these failures.

Sure! Please find them attached. I retried with no jobs parameter as
well, same issues.

I did some more bisecting of my git settings. And now it's getting
embarrassing...

Can you reproduce it if you do

git config core.commitGraph false
git config fetch.writeCommitGraph true
?

If I flip core.commitGraph to true I don't get an error anymore.