From: Ben Maurer <bmaurer@fb.com>
Date: Mon, 06 Jan 2014 21:15:04 GMT
Subject: RE: [PATCH] [RFC] Making use of bitmaps for thin objects
Message-ID: <5CDDBDF2D36D9F43B9F5E99003F6A0D4466883DF@PRN-MBX02-1.TheFacebook.com>
In-Reply-To: <20140106145723.GA15489@sigill.intra.peff.net>

> Sorry for the slow reply; I've been on vacation.

No worries.

> When you build your bitmaps, do you set the pack.writeBitmapHashCache
> option? We found that it makes a significant difference during the
> compression phase, as otherwise git attempts deltas between random files
> based on size. Here are some numbers for a simulated fetch from
> torvalds/linux, representing about 7 weeks of history. Running:

Yeah, I enabled this option. I don't have timings for generating the bitmap index without this option unfortunately (this is a pretty large repo, doing the full repack that I needed to do to generate the first version took 15+ minutes)

> Having been confused by it myself before, I think the magic keyword is
> "preferred base". Once you know that, the code makes more sense. :)

Ah, nice! That was pretty confusing :-)

> Let me know how this patch does for you. My testing has been fairly
> limited so far.

This patch looks like a much cleaner version :-). Works well for me, but my test setup may not be great since I didn't get any errors from completely ignoring the haves bitmap :-).