Re: I have end-of-lifed cvsps

From: Eric S. Raymond <esr@thyrsus.com>
Date: Dec 17, 2013, 14:58 UTC
Message-ID: <20131217145809.GC15010@thyrsus.com>
In-Reply-To: <CALKQrgf3kuXRpbWmSp_nk8+zDFYNzkgV+dSBHaBbmUkxqjaDUA@mail.gmail.com>

Johan Herland <johan@herland.net>:

Show 9 quoted lines

> HOWEVER, this only solves the "cheap" half of the problem. The reason
> people want incremental CVS import, is to avoid having to repeatedly
> convert the ENTIRE CVS history. This means that the CVS exporter must
> learn to start from a given point in the CVS history (identified by
> the above mapping) and then quickly and efficiently convert only the
> "new stuff" without having to consult/convert the rest of the CVS
> history. THIS is the hard part of incremental import. And it is much
> harder for systems like CVS - where the starting point has a broken
> concept of history...

I know of *no* importer that solves what you call the "deep" part of the problem. cvsps didn't, cvs-fast-import doesn't, cvs2git doesn't. All take the easy way out; parse the entire history, and limit what is emitted in the output stage.

Actually, given what I know about delta-file parsing I'd say a "true" incremental CVS exporter would be so hard that it's really not worth the bother. The problem is the delta-based history representation. Trying to interpret that without building a complete set of history states in the process (which is most of the work a whole-history exporter does) would be brutally difficult - barely possible in principle maybe, but I wouldn't care to try it.

It's much more practical to tune up a whole-history exporter so it's acceptably fast, then do incremental dumping by suppressing part of the conversion in the output stage.

cvs-fast-export's benchmark repo is the history of GNU troff. That's 3057 commits in 1549 master files; when I reran it just now the whole-history conversion took 49 seconds. That's 3.7K commits a minute, which is plenty fast enough for anything smaller than (say) one of the *BSD repositories.

-- 
		<a href="http://www.catb.org/~esr/">Eric S. Raymond</a>