From: Junio C Hamano <junkio@cox.net>
Date: Fri, 24 Mar 2006 10:21:25 GMT
Subject: Re: [PATCH] cogito: Avoid slowness when timewarping large trees.
Message-ID: <7vd5gc16u2.fsf@assigned-by-dhcp.cox.net>
In-Reply-To: <20060324084423.GA30213@coredump.intra.peff.net>

Jeff King <peff@peff.net> writes:

> tree_timewarp was calling read, egrep, and rm in an O(N) loop where N is
> the number of changed files between two trees. This caused a bottleneck
> when seeking/switching/merging between trees with many changed files.
>...
> ---
>
>  cg-Xlib |    9 +++------
>  1 files changed, 3 insertions(+), 6 deletions(-)
>
> a9a160c0bd63973c53ba3aa74650728135d23ac7
> diff --git a/cg-Xlib b/cg-Xlib
> index a2f28cf..ceddeeb 100644
> --- a/cg-Xlib
> +++ b/cg-Xlib
> @@ -345,12 +345,9 @@ tree_timewarp()
>  
>  	# Kill gone files
>  	git-diff-tree -r "$base" "$branch" |
> ...
> +		# match ":100755 000000 14d43b1abf... 000000000... D"
> +		sed -ne 's/^:\([^ ][^ ]* \)\{4\}D\t//p' |
> +		xargs rm --
>  	git-checkout-index -u -f -a

Metainformation fields are internally separated with SP and a
TAB comes before pathname; you can just say:

	sed -ne 's/^:[^	]* D	//p'

there (whitespace inside [] and after D are TAB; one before D is
a SP).  You might also want to consider "xargs rm -f --", BTW.

However, I wonder why it does not do this instead:

	... stash away the local changes
	git-read-tree -m "$base" ;# reset the index to $base

	# switch to $branch -- removing gone files as well
	git-read-tree -m -u "$base" "$branch"

Then you can also lose diff-tree and checkout-index there.