Re: git-rev-list: add "--dense" flag

On Sat, 22 Oct 2005, Petr Baudis wrote:

quoted

If you're just going to feed them to diff-tree _anyway_, then you might as 
well not even do the dense thing, because quite frankly, you're just doing 
extra work.

fork() is awfully expensive for me. fork()ing something (supposedly)
trivial (it was stat) slowed my (non-trivial) loop about 4 times.

Not fork. More like

	git-rev-list .. | git-diff-tree --stdin

If you do it that way (which is quite common - git-whatchanged, git-log 
etc), there's no reason to ask for a dense output, because git-diff-tree 
can handle the non-dense one as fast as git-rev-list can.

But the --dense option is wonderful for "gitk", and for "slow stuff". 
Where "slow" can indeed be a fork, or just an interpreter loop like a 
shell/perl script, which would fork/exec git-diff-tree for each commit.

From a commit-list standpoint

	git-rev-list --dense ... -- paths

is the same as

	git-rev-list -- paths | git-diff-tree -s -r --stdin -- paths

but it's somewhat more efficient, and more importantly, it rewrites the 
parents. So quite often, you'd want to use "--dense" together with 
"--parent" so that you get the "rewritten" history. That's how come gitk 
didn't need any changes, and it "just worked". It's also how my example 
script did the rename detection without having to traverse unnecessary 
commits.

		Linus