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Re: Which repository technology

From: Mark Phippard <MarkP_at_softlanding.com>
Date: 2005-05-21 17:55:34 CEST

> do folks have any general recommendations about the choice
> between BDB and FSFS repository technologies?

I think most people would recommend FSFS, especially for a newb. While BDB
itself is a solid technology, the way that Subversion uses it makes it sort
of "fragile". If everything is setup right, in terms of permissions, it
will be rock-solid and you will probably never have a problem. But if you
do not really know what you are doing it is easy to make a mistake and
"wedge" the repository. As it stands right now, BDB does not offer any
compelling reasons to be used over FSFS. FSFS repositories are smaller and
less prone to problems. Except for a few cases, they seem to be generally
faster and they offer some interesting options for setting up permissions
and performing backups since the repository files are immutable.

> - At least it's possible to recover a Berkeley db

This isn't really a feature. Recovery isn't fixing the sort of problems
you think it is, it merely fixes BDB itself so that you can get the
repository working again. In theory, FSFS repositories should not get into
this state.

> "Scalability: number of revision trees: some older
> native filesystems don't scale well with thousands of entries in a single
> directory."

This does appear to be a real problem in practice. It is easily solvable
in the future if needed. This issue doesn't appear to effect Subversion at
all, it is possible it would have an impact on utilities that want to scan
the directory, like a backup routine, or browsing the repository folder
using something like Windows Explorer. The Subversion server process are
not effected by this at all.

> - FSFS's "diffs only" storage mechanism seems intuitively more fragile in
> the long run.

Since the repository files are immutable this sort of problem can only
happen at the disk storage level, unless someone tampers with the files.
In either case, BDB would be at least as susceptible to the same problems.
FSFS's skip-delta architecure is one of its best features. It would be
interesting to see how the BDB back-end might improve if this technique
were applied to it.

Anyway, go with FSFS. I hope this helps.


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Received on Sat May 21 17:57:19 2005

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