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FSFS packing functionally complete

From: Hyrum K. Wright <hyrum_wright_at_mail.utexas.edu>
Date: Wed, 26 Nov 2008 20:11:16 -0600

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.


Received on 2008-11-27 03:12:25 CET

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