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Re: skels in string table

From: Ben Collins-Sussman <sussman_at_red-bean.com>
Date: Wed, 11 Jun 2008 16:49:33 -0500

On Wed, Jun 11, 2008 at 4:45 PM, Karl Fogel <kfogel_at_red-bean.com> wrote:
> "Vyacheslav V. Zholudev" <vyacheslav.zholudev_at_gmail.com> writes:
>> Hello!
>> I'm digging into BDB backend and thought that strings "table" can
>> contain only either full text or deltas, but I found out that smth
>> like:
>> "((ins.xml 5 6.0.7) (install_log.xml 5 4.0.5) (cp.xml 5 7.0.8))"
>> is written to the strings table as a fulltext, which reminds me some
>> skel. Or is it smth else? If yes, how can i distinguish whether the
>> full content of file is written or smth else?
>> Thanks in advance!
> Vyacheslav,
> Since directories are just lists of entries anyway, we represent them
> using the same skel syntax used for reps metadata -- so that's how
> skel-like data ends up in the strings table.
> Each subcell above is a directory name followed by the name of its node
> revision (the name is a string, so the length comes first, followed by a
> space; see subversion/libsvn_fs_base/util/skel.h for details, but you've
> probably already read that file :-) ).

Alas, this design doesn't scale well when you have versioned
directories with thousands of children. Every attempt to add, delete,
or modify a child in the directory causes the *entire* list of dirents
to be loaded into memory, then serialized back to disk again. As the
number of children in the directory increases, it becomes O(N^2) to to
modify them.

I'm dreaming of fixing this someday... perhaps by splitting up a
directory's dirents across multiple string-keys.

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Received on 2008-06-11 23:49:48 CEST

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