Re: Terrible bad performance for it blame --date=iso -C -C master -- <file>

From: Junio C Hamano <gitster@pobox.com>
Date: Mar 31, 2017, 15:52 UTC
Message-ID: <xmqq60ip1m0f.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <58DE0598020000A1000256CE@gwsmtp1.uni-regensburg.de>

"Ulrich Windl" <Ulrich.Windl@rz.uni-regensburg.de> writes:

Show 11 quoted lines

> I was running "vc-annotate" in Emacs for a file from a large
> repository (>40000 files, a big percentage being binary, about 10
> commits). For the first file the result was presented rather soon, but
> for a second file the command did not finish even after about 10
> minutes!
>
> The file in question is a rather short text file (124 kB), and
> according to git log it has one commit.
>
> While being bored, I did an strace of the command to find out that a
> huge number of files is inspected.

With -C -C the user (vc-annotate?) is asking to inspect huge number of files, to find if the contents of the file (except for the part that came from its own previous version) came from other existing files. So this is very much expected.

It might not be a bad idea to teach "blame" not to pay attention to any path that is marked as "-diff" (e.g. binary files) when trying to see if remaining contents appeared by borrowing from them. We do not have that heuristics (yet).