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Re: A modest proposal: No index or "log -g" in Subversion 1.5

From: David Glasser <glasser_at_davidglasser.net>
Date: 2007-11-30 03:45:24 CET

On Nov 29, 2007 6:04 PM, Hyrum K. Wright <hyrum_wright@mail.utexas.edu> wrote:
> > * I have a completely working implementation for FSFS that keeps
> > enough metadata in the DAG itself to answer that question
> > efficiently. So we really don't need to use sqlite for that.
> > It would probably require a db format bump, but that's not too big a
> > deal (and wouldn't really need a dump/load; I can give more details
> > if you want). Hopefully the BDB implementation wouldn't be hard
> > either.
>
> Having this metadata would be very useful. The entire reason we are
> using the mergeinfo index to look up child paths, is because we wanted
> to avoid doing a recursive walk through the directory structure for
> *every single revision* of a given path. If we need to eliminate the
> mergeinfo index and/or we find a better way to capture this data, I'll
> be the first one in line to use it.

Indeed, and I suspect that the directions Kamesh is going will get
that. But I also expect that working out the details will take a
while, and it can be added in 1.6 (possibly requiring a dump-and-load,
though).

> > * My implementation does a little more error-checking than the sqlite
> > implementation; specifically, the sqlite implementation didn't care
> > if you asked for mergeinfo about paths that don't exist, whereas
> > mine does (though it could suppress that error, of course). That
> > extra checking is already showing me a bunch of bugs all throughout
> > the client code, and especially in "log -g", where they're passing
> > in the wrong paths.
> >
> > * Kamesh's issue-2897 branch would require more sophisticated queries.
> > (And in fact I think that those queries might enable "log -g" to do
> > its job better.) But it's controversial whether or not we should
> > try to get issue 2897 in for 1.5; it's a big, big problem with no
> > simple answer. In addition, this would require us to fix the
> > serious bugs in the sqlite index mentioned above.
> >
> > I would like to propose the following:
> >
> > * We do not attempt to solve Issue 2897 for 1.5. It is probably
> > possible to solve it, but it will take a lot of work, have lots of
> > subtleties, etc.
> >
> > * We disable "log -g" for 1.5. "log -g" was originally proposed as a
> > 1.6 command; it only switched to 1.5 because Hyrum finished his
> > implementation. (And there are a lot of good things about log -g; I
> > certainly have respect for Hyrum's work, and expect that 1.6 could
> > contain a fixed version of it.) This would allow us to ignore the
> > "log -g" bugs for now and focus on bugs more central to merge
> > tracking as opposed to just this one auditing feature.
>
> I'll be honest: "log -g" is kinda my baby (Summer of Code and all that).
> It's a baby with warts, a few extra legs, and a deep burlesque voice,
> but still my baby. :) However, I have absolutely *no reservation* about
> pulling it (I'll even do the grunt work), if that means a better, sooner
> 1.5. There may be some issues with "log -g" which can't get resolved
> until 2.0, and I'm fine with that.
>
> I haven't looked at the bugs Dave mentions, so I don't know what kind of
> effort would be involved with getting them fixed. "blame -g" does not
> use the index beyond getting the mergeinfo for PATH@REV, so it should be
> relatively safe from any mucking we do with the index. "blame -g"
> probably has bugs of it's own, though. :)

My guess is that the bugs are not unfixable, but that that probably
wouldn't exist at all if "log -g" got to use better information than
the current index. And I'd rather make that better information happen
in 1.6 than in 1.5.

And yes, I should have mentioned that I think "blame -g" is unaffected here.

> > * Because we no longer need it, we remove the sqlite mergeinfo index
> > from 1.5. This reduces a huge amount of code complexity in the FS
> > backends, and lets us not worry about fixing the bugs in keeping the
> > indices up to date. Because we don't need it, we don't use my
> > extra-metadata-in-DAG thing either.
> >
> > When working on 1.6, we can solve #2897 and fix "log -g" with much
> > more leisure to get it right. If fixing them requires retrying the
> > sqlite index again, or my metadata idea, then so be it: we can add
> > that code back in in 1.6 (it's all in version control) and make it
> > work for those needs then.
> >
> > But I think we can make 1.5 much more solid and less complex by simply
> > deferring #2897 and "log -g" to 1.6. 1.5 will still have a superset
> > of svnmerge.py's features.
> >
> > (I don't mean to disrespect the hard work done on the sqlite backend,
> > "log -g", or issue-2897 here. I just think that these are difficult
> > problems to solve, and that making a release that doesn't try to solve
> > them and fixing them with more leisure is better than trying to do
> > everything at once and being full of bugs.)
>
> I'd like to echo the concern Karl brought up elsethread. If we do yank
> a couple of features, we need to be very open about what 1.5 is and
> isn't. We've been touting 1.5 a long time, and lots of folks have been
> looking forward to it. If we start yanking features, we need to be
> *very careful* about managing expectations, and helping people know
> what's in 1.5, and what will be coming later.

Absolutely.

--dave

-- 
David Glasser | glasser_at_davidglasser.net | http://www.davidglasser.net/
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Received on Fri Nov 30 03:45:39 2007

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