Re: [PATCH] blame.c: don't drop origin blobs as eagerly

From: Duy Nguyen <pclouds@gmail.com>
Date: Apr 3, 2019, 12:06 UTC
Message-ID: <CACsJy8BCGHqjO5fKG7TO5X239z_7Gzdo80jF0rx939X501yVnA@mail.gmail.com>
In-Reply-To: <20190403113604.GA2941@sigill.intra.peff.net>

On Wed, Apr 3, 2019 at 6:36 PM Jeff King <peff@peff.net> wrote:

Show 5 quoted lines

> I suspect we could do even better by storing and reusing not just the
> original blob between diffs, but the intermediate diff state (i.e., the
> hashes produced by xdl_prepare(), which should be usable between
> multiple diffs). That's quite a bit more complex, though, and I imagine
> would require some surgery to xdiff.

Amazing. xdl_prepare_ctx and xdl_hash_record (called inside xdl_prepare_ctx) account for 36% according to 'perf report'. Please tell me you just did not get this on your first guess.

I tracked and dumped all the hashes that are sent to xdl_prepare() and it looks like the amount of duplicates is quite high. There are only about 1000 one-time hashes out of 7000 (didn't really draw a histogram to examine closer). So yeah this looks really promising, assuming somebody is going to do something about it.

-- 
Duy