[PATCH 11 of 11 V1] store: implement new fncache2 requirement

[Bryan O'Sullivan]

On Tue, Oct 2, 2012 at 2:07 PM, Matt Mackall <mpm at selenic.com> wrote:

> On the other hand, the only thing pushing this particular change is
> performance, so I'm in no great hurry to make a switch.
>

I wrote a local patch that enables fncache2, and so far it's behaving
itself.


> I'd rather
> gather up a few more format improvements to go with it (for instance,
> dropping all the redundant data/ and .i in .hg/store/fncache).
>

That doesn't sound like an improvement to me.

It would save a few bytes per entry, for a total space savings of 14% in
the repos I looked at.

On the other hand, as far as I can tell, it would increase the amount of
work we have to do per entry forever after: we'd have to tack "data/" and
".i" back on, either when writing or reading the fncache file, or when
looking entries up.

We already know that fncache performance is hugely important, so the bar
for doing extra computation should be very high.
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