Re: [PATCH v2] packed-refs: use `fwrite()` when passing refs verbatim

[Toon Claes <toon@iotcl.com>]

Karthik Nayak <karthik.188@gmail.com> writes:

> The `write_with_updates()` function uses a `struct ref_iterator` to
> iterate over all refs to write to the temporary packed-refs file. It
> receives the iterator from `packed_ref_iterator_begin()` which takes a
> snapshot of the 'packed-refs' file.
>
> While writing to the new packed-refs file, writes are routed via
> `write_packed_entry()` which uses `fprintf()`. Even for references which
> haven't changed, we use the same mechanism. Instead, let's track the
> position of unchanged references in the snapshot iterator and directly
> use `fwrite()`.
>
> With this, any sanitation which was happening as a side of reformatting

s/side/side effect/ ?

> is now lost. But that was never the job of this section of the code,
> since the main intention is to simply rewrite the remaining refs post
> deletion of the selective few.

Agreed.

>
> This removes the unnecessary formatting operation involved. We can see a
> consistent ~20% performance improvement when deleting from packed
> references.
>
> Benchmark 1: update-ref: delete ref (refcount = 100000, revision = master)
>   Time (mean ± σ):      28.7 ms ±   1.7 ms    [User: 22.5 ms, System: 5.9 ms]
>   Range (min … max):    26.7 ms …  33.3 ms    46 runs
>
> Benchmark 2: update-ref: delete ref (refcount = 100000, revision = b4/kn-speedup-packed-refs)
>   Time (mean ± σ):      23.8 ms ±   1.2 ms    [User: 17.5 ms, System: 6.0 ms]
>   Range (min … max):    22.1 ms …  27.7 ms    56 runs
>
> Summary
>   update-ref: delete ref (refcount = 100000, revision = b4/kn-speedup-packed-refs) ran
>     1.21 ± 0.09 times faster than update-ref: delete ref (refformat = files, refcount = 100000, revision = master)
>
> Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
> ---
> Changes in v2:
> - Instead of using the existing function, introduce a new
>   `write_packed_entry_raw()`.
> - Modify the commit to also note that we lose sanitization.

s/commit/commit message/

> - Link to v1: https://patch.msgid.link/20260930-kn-speedup-packed-refs-v1-1-111cd03d9b0e@gmail.com

Okay, I'm okay with this version.

-- 
Laters,
Toon