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Re: FSFS packing functionally complete

From: Julian Foad <julianfoad_at_btopenworld.com>
Date: Thu, 27 Nov 2008 19:49:32 +0000

On Thu, 2008-11-27 at 03:17 -0800, Blair Zajac wrote:
> Hyrum K. Wright wrote:
> > Hi all.
> >
> > As of r34446, the implementation of packing on fsfs is functionally complete on
> > the fsfs-pack branch. For those that don't know, packing consists of mushing
> > all the individual rev files in a completed shard into one file, thus
> > eliminating the inode penalty for that entire shard. Packing a trunk-generated
> > copy of the ASF repository saved about 1 GB on a 24 GB repo. There may be
> > additional performance benefits in dealing with a much smaller set of rev files
> > (OS caching, etc.), but I haven't yet investigated that.
> >
> > This comes at a cost: the offsets of revisions in the pack file are stored
> > separately, and thus require an additional open/seek to get that information.
> > Also, determining whether a revision is stored in a pack file or not also
> > requires additional I/O. I think that most of this can be eliminated with
> > caching and heuristics, but those haven't yet been implemented.
> >
> > I'm not currently planning on including this functionality in 1.6, as it's kinda
> > biggish feature, the optimizations aren't yet in place, and I feel like merging
> > right before we branch 1.6.x could be a bit destabilizing. However, I could
> > easily be talked into it. :)
> >
> > Anyway, I'm soliciting feedback on the implementation and usage of this feature.
> > Comments welcome.
> This is something I'll definitely need. We're going to be having multiple
> repositories each with a million revisions, so having fsfs packing will make the
> repository much easier to work with. Also, any fsck's will be much faster :)
> So +1 for merging into trunk from me.

Do we have any cost/benefit numbers to demonstrate the "much easier to
work with", or a qualitative description that you could point me to? I
couldn't find anything by searching for "pack" or "inode" in the mail

- Julian

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Received on 2008-11-27 20:49:51 CET

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