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Why is git log on large repos slower when outputting to tty?

Subject: Why is git log on large repos slower when outputting to tty?

## tl;dr

3 messages between Oct 17, 2024 and Oct 18, 2024.

replies: 2people: 2as markdown or json

Jeff King· Oct 18, 2024, 04:22 UTC · re: Henry Qin · lore

Re: Why is git log on large repos slower when outputting to tty?

On Thu, Oct 17, 2024 at 10:46:17AM -0700, Henry Qin wrote:
> Details in my Stackoverflow question:
> 
> https://stackoverflow.com/questions/79099095/why-is-git-log-significantly-slower-when-outputting-to-a-tty

My first thought was "decorations", and indeed somebody gave that answer in the stack overflow thread. The default for log.decorate is "auto", which will turn them on when output is to a tty. You can set it to "false" to disable it.

As for why decorations are slow: it is necessarily going to be at least linear in the number of refs, since we have to build the reverse mapping up front. Do you have a lot of refs? What does "git for-each-ref | wc -l" say?

-Peff
Henry Qin· Oct 18, 2024, 04:28 UTC · re: Jeff King · lore

Re: Why is git log on large repos slower when outputting to tty?

Hi Jeff,

Thanks for your reply! This was actually discussed in the comment thread on SO as well. Yes, I do have 15618 refs in that repo, and turning off decoration indeed fixed the performance issue!

Thanks, ~Henry

On Thu, Oct 17, 2024 at 9:23 PM Jeff King <peff@peff.net> wrote:
Show 18 quoted lines
>
> On Thu, Oct 17, 2024 at 10:46:17AM -0700, Henry Qin wrote:
>
> > Details in my Stackoverflow question:
> >
> > https://stackoverflow.com/questions/79099095/why-is-git-log-significantly-slower-when-outputting-to-a-tty
>
> My first thought was "decorations", and indeed somebody gave that answer
> in the stack overflow thread. The default for log.decorate is "auto",
> which will turn them on when output is to a tty. You can set it to
> "false" to disable it.
>
> As for why decorations are slow: it is necessarily going to be at least
> linear in the number of refs, since we have to build the reverse mapping
> up front. Do you have a lot of refs? What does "git for-each-ref | wc
> -l" say?
>
> -Peff

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