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Re: Idea for libsvn_wc after 1.0 ...

From: Greg Hudson <ghudson_at_MIT.EDU>
Date: 2004-02-10 13:12:27 CET

On Tue, 2004-02-10 at 06:17, Ph. Marek wrote:
> > con: the WC loses platform independence (i.e., you can't share it and
> > expect it to work under linux, mac, and windows).
> I'd expect to have a processor-dependence, ie. big vs. little-endian.
> Is the db-format different between linux/windows/MacOS/etc.???

BDB application data is stored in a platform-independent file. Since
Subversion's application data is itself platform-independent, the actual
files like "nodes" are platform-independent.

However, to access BDB data, you must mmap() a file as a region of
shared memory and treat some of the contents as pthread_mutex_t
structures. (On Windows, something equivalent happens.) Since no
shared filesystem can implement mmap() in a sane manner, you cannot use
BDB on a shared filesystem, no matter how well it implements POSIX
locking semantics. Moreover, you cannot copy a database from one
platform to another and have it work, unless the platforms have
identical memory representations of pthread_mutex_t and some other
structures.

Your proposal would have more applicability if we had a filesystem
back-end without so many restrictions. I hope to create such a back end
some day, perhaps next winter. (My real job tends to get busy in the
spring and summer. Of course, other people are also welcome to have a
go at this task, and I can contribute ideas, but it's a pretty big
undertaking.)

At any rate, as clkao points out, you should look into svk. I think
it's very close to what you propose.

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Received on Tue Feb 10 13:13:10 2004

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