Re: [PATCH] git-completion.bash: always swallow error output of for-each-ref

From: Junio C Hamano <gitster@pobox.com>
Date: Feb 4, 2016, 19:06 UTC
Message-ID: <xmqqwpqki9bh.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <alpine.DEB.2.20.1602041216240.2964@virtualbox>

Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:

Show 20 quoted lines

>> $ time git for-each-ref --format='%(refname:short)' refs/tags >/dev/null
>> 
>> real    0m0.009s
>> user    0m0.004s
>> sys     0m0.004s
>
> And the timings in the ticket I mentioned above are not pretty small:
> 0.055s vs 1.341s
>
>> The upcoming refname:strip does much better:
>> 
>> $ time git for-each-ref --format='%(refname:strip=2)' refs/tags >/dev/null
>> 
>> real    0m0.004s
>> user    0m0.000s
>> sys     0m0.004s
>
> This is funny: after reading the commit message at
> https://github.com/git/git/commit/0571979b it eludes me why strip=2 should
> be so much faster than short...

"short" tries to ensure that the result is not ambiguous within the repository, so when asked to shorten refs/heads/foo, it needs to check if refs/tags/foo exists. "strip=2" textually strips two levels from the top without worrying about ambiguity across different hierarchies.