Re: [PATCH v2] read_index_from(): Skip verification of the cache entry order to speed index loading

[Alex Vandiver <alexmv@dropbox.com>]

On Mon, 30 Oct 2017, Jeff King wrote:
> On Mon, Oct 30, 2017 at 08:48:48AM -0400, Ben Peart wrote:
> 
> > Any updates or thoughts on this one?  While the patch has become quite
> > trivial, it does results in a savings of 5%-15% in index load time.
> 
> I like the general direction of avoiding the check during each read.

Same -- the savings here are well worth it, IMHO.

> > I thought the compromise of having this test only run when DEBUG is defined
> > should limit it to developer builds (hopefully everyone developing on git is
> > running DEBUG builds :)).  Since the test is trying to detect buggy code
> > when writing the index, I thought that was the right time to test/catch any
> > issues.
> 
> I certainly don't build with DEBUG. It traditionally hasn't done
> anything useful. But I'm also not convinced that this is a likely way to
> find bugs in the first place, so I'm OK missing out on it.

I also don't compile with DEBUG -- there's no documentation that
mentions it, and I don't think I'd considered going poking for what
was `#ifdef`d.  I think it'd be reasonable to provide some
configure-time setting that adds `CFLAGS="-ggdb3 -O0 -DDEBUG"` or
similar, but that seems possibly moot for this particular change (see
below).

> But what we probably _do_ need is to make sure that "git fsck" would
> detect such an out-of-order index. So that developers and users alike
> can diagnose suspected problems.

Agree -- that seems like a better home for this logic.

> > I am working on other, more substantial savings for index load times
> > (stay tuned) but this seemed like a small simple way to help speed
> > things up.

I'm interested to hear more about what direction you're looking in here.
 - Alex