Original failed to include the note that this patch is for the 'next' branch, my apologies.
> -----Original Message-----
> From: Roger Strain <rstrain@xxxxxxxx>
> Sent: Friday, October 12, 2018 8:52 AM
> To: git@xxxxxxxxxxxxxxx
> Cc: Strain, Roger L. <roger.strain@xxxxxxxx>
> Subject: [PATCH] subtree: performance improvement for finding
> unexpected parent commits
>
> After testing a previous patch at larger scale, a performance issue was
> detected when using git show to locate parent revisions, with a single run of
> the git show command taking 2 seconds or longer in a complex repo.
> When the command is required tens or hundreds of times in a run of the
> script, the additional wait time is unaccepatable. Replacing the command
> with git rev-parse resulted in significantly increased performance, with the
> command in question returning instantly.
>
> Signed-off-by: Roger Strain <rstrain@xxxxxxxx>
> Thanks-to: Junio C Hamano <gitster@xxxxxxxxx>
> ---
> contrib/subtree/git-subtree.sh | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/contrib/subtree/git-subtree.sh b/contrib/subtree/git-subtree.sh
> index 1c157dbd9..147201dc6 100755
> --- a/contrib/subtree/git-subtree.sh
> +++ b/contrib/subtree/git-subtree.sh
> @@ -633,7 +633,7 @@ process_split_commit () {
> else
> # processing commit without normal parent information;
> # fetch from repo
> - parents=$(git show -s --pretty=%P "$rev")
> + parents=$(git rev-parse "$rev^@")
> extracount=$(($extracount + 1))
> fi
>
> --
> 2.19.1
