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

From: Samuel Lijin <sxlijin@gmail.com>
Date: Mar 31, 2017, 16:23 UTC
Message-ID: <CAJZjrdXyRqs=oscynWghB13OiR8qjP10O2EV-wiP-acb7wqY-A@mail.gmail.com>
In-Reply-To: <xmqq60ip1m0f.fsf@gitster.mtv.corp.google.com>

Hi Ulrich,

Is there any chance you could share the repo where this is coming from?

This is actually something a colleague and I are looking into seeing if we can crunch out some performance gains since -C -C isn't threaded.

Sam

On Fri, Mar 31, 2017 at 10:52 AM, Junio C Hamano <gitster@pobox.com> wrote:

Show 23 quoted lines

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