Re: [Summit topic] Let's have chalk talks (part 1/?)

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

On Mon, Oct 25 2021, Philip Oakley wrote:

> On 22/10/2021 08:51, Johannes Schindelin wrote:
>> Apparently I have to send this in chunks, to fool the Bayes filter of our
>> beloved mailing list into doing The Right Thing.
>>
>> This session was led by Emily Shaffer. Supporting cast: Ævar Arnfjörð
>> Bjarmason, brian m. carlson, CB Bailey, and Junio Hamano.
>>
>> Notes:
>>
>>  1.  What’s a public chalk talk?
>>
>>      1.  At Google, once a week, the team meets up with no particular topic in
>>          mind, or a couple topics, very informal
>>
>>      2.  One person’s turn each week to give an informal talk with a white
>>          board (not using chalk)
>>
>>      3.  Topic should be technical and of interest to the presenter
> [...]
>
> A 'listener' perspective..
>
> At the summit, the packfile's packing algorithm was mentioned as a
> historic 'chalk talk' that's now in the technical documentation.
>
> In the meantime, while chatting to a colleague about the birthday
> paradox and its relation to Bloom filters, I realised I didn't
> understand what our Bloom filters were trying to do and what they recorded.
>
> I had a look at the code and documentation, but there isn't much there
> about our Bloom filter implementation. A chalk talk could later be used
> in the same manner as the packfile discussion to show what the filters do?
>
> If there is someone who'd like to talk through what the Bloom filters
> are doing in Git then I'd be all ears.

That sounds like a good idea for a topic, not to take away from any of
that discussion, but I believe the bloom filters we have are exclusively
used for path filtering if they exist in the commit-graph.

I.e. for:

    git rev-list -- $path

See c525ce95b46 (commit-graph: check all leading directories in changed
path Bloom filters, 2020-07-01) for one use-case and benchmark numbers.