On Thu, May 24, 2012 at 06:54:56PM -0600, Martin Fick wrote: > > Yes, exclusively warm. And all of the refs were packed, > > which makes the warm/cold difference less interesting > > (it's one 30MB or so file). I don't think there's much > > point in thinking about the performance of 400K loose > > refs (which would be absolutely horrific cold-cache on > > most traditional filesystems). If you have that many, > > you would want to keep the bulk of them packed. > > Mostly true, except for one strange case still I think? > > When cloning a gerrit repo, users to not get the changes > since they are not under refs/heads but refs/changes. So > later, if they choose to fetch refs/changes/*, all of those > new incoming refs are loose. Hmm. Yeah, clone will always write a packed-refs file, but I think "git fetch" will always write loose refs, under the assumption that the former will be getting a lot more refs than the latter. But of course that is only a guess. It would be nice if fetch could fetch straight into packed refs if we are getting more than N items. We'd have to give some thought to potential race conditions, though. Usually pack-refs isn't modifying the ref, so it can just write out the value to the packed-refs file, then delete the loose ref if nobody has touched it since we wrote. But here we're combining it with a modification, so I suspect there would be a race with another process trying to modify it. > Yes, someone should pack those > refs right away, but I think it actually churns the hell out > of my disk and takes a significant amount of time during the > initial fetch. I am not certain about this, and the > behavior may depend on the filesystem in use, but I think > that this time might even be asynchronous (journals and > all), it feels like my disk keeps churning for a while even > after this is over. I believe that this might still be the > worst case left with refs, and it can be pretty bad, Yeah, I wouldn't be surprised if this thrashes your disk. Writing hundreds of thousands of 40-byte files is one of the most awful loads for many filesystems, since each file gets its own inode. I haven't tried btrfs, but my impression is that it can magically pack the data from many files into one node. -Peff -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html