Re: [PATCH] check_refname_component: Optimize

From: Jeff King <peff@peff.net>
Date: May 30, 2014, 17:29 UTC
Message-ID: <20140530172944.GC25443@sigill.intra.peff.net>
In-Reply-To: <538853B5.1080308@alum.mit.edu>

On Fri, May 30, 2014 at 11:47:33AM +0200, Michael Haggerty wrote:

Show 12 quoted lines

> > I could guess something like "the writer has a different idea of what a
> > valid refname is than we do". But that applies as well to (2), but just
> > as "the reader who wrote packed-refs.stat has a different idea than we
> > do".
> 
> If we want to be robust to future changes to refname rules, we could add
> a header flag like
> 
>     # pack-refs with: peeled fully-peeled check-level=1.0
> 
> which promises that the reference names in the file conform to the
> current ("version 1.0") check_refname_format() rules.

Yeah, I thought about mentioning something like that. But really, this just seems like a lot of complexity to solve the problem in a wrong way.

It's not running check_refname_format that is the real problem. It's the fact that we do O(# of refs) work whenever we have to access the packed-refs file. check_refname_format is part of that, surely, but so is reading the file, creating all of the refname structs in memory, etc.

I'd much rather see a solution that lets us do O(log N) or O(1) work to access a ref, and then we don't have to care about optimizing check_refname_format specifically.

I don't mind internal code speedups to micro-optimize check_refname_format. They may make the code uglier, but they're fairly contained. But things like check-level are much more invasive, and we'll need to keep compatibility with them in future versions.

-Peff