Re: [PATCH] subtree: performance improvement for finding unexpected parent commits
From: Junio C Hamano <hidden>
Date: 2018-10-12 14:22:12
Roger Strain [off-list ref] writes:
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 <redacted> Thanks-to: Junio C Hamano [off-list ref]
That usually is spelled as "Helped-by:". Will queue. Thanks. I still find it disturbing not to know why "show -s --format=..." takes measurable time, though. "-s" means "we do not need any diff output", so it ought to be comparable to "git cat-file commit $rev" with some formatting, but apparently your repository is making Git spend a lot more than that. Puzzled...
quoted hunk
--- contrib/subtree/git-subtree.sh | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/contrib/subtree/git-subtree.sh b/contrib/subtree/git-subtree.sh index 1c157dbd9..147201dc6 100755 --- a/contrib/subtree/git-subtree.sh +++ b/contrib/subtree/git-subtree.sh@@ -633,7 +633,7 @@ process_split_commit () { else # processing commit without normal parent information; # fetch from repo - parents=$(git show -s --pretty=%P "$rev") + parents=$(git rev-parse "$rev^@") extracount=$(($extracount + 1)) fi