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Re: [Gnu-arch-users] Re: Working out a branching scheme [was: tag --seal

From: James Blackwell
Subject: Re: [Gnu-arch-users] Re: Working out a branching scheme [was: tag --seal --fix]
Date: Sun, 4 Apr 2004 23:23:36 -0400

> Having 10'000 revisions on a single branch is something that people
> want to do with CVS, and will want to do with arch.  If arch is to be
> useful for those people, it should be able to deal gracefully with
> that sort of thing.

> If you think those people are wrong in wanting to do that, your answer
> should hopefully be ``that's insane, but arch will handle it just fine.''

Arch "works fine" with thousands of revisions in one branch. In fact,
there are already a small handful of archives that already do this. 

For example, Robert Collins has converted the entire cvs history of
automake into arch, which has thousands of revisions. 

Arch handles the large number of revisions gracefully, gradually slowing
down as more and more revisions are added.

> (Another thing which I find arch unsuitable for is hacking at a large
> remote tree when you don't have much local disk space.  I spent a few
> years working on a 300 MB tree with a laptop with 4 GB local disk,
> typically none of which was free; that would not have been possible
> with arch.)

This problem is already in the past and as time continues to march on,
the problem will fade even further. Today, 300 megabytes is a large archive;
seven years ago it was *huge*.

These are facts:

   1. archives grow linearly, with a shallow slope.
   2. drive space grows nonlinerarly, doubling every 2 years or so.
   3. Arch is ready for all but the very largest archives *today*
   4. The average archive size today is 16MB.
   5. The average revision size is about 50K (the median is 17K) 
   6. The average archive has 11 versions

We can probably agree on this:

   7. A project is 'very popular' if it averages 220 revisions a day 
      (or 20 revisions for each of its 11 versions)

                               Today    Two years        Four Years
Archive size                   16MB     23.3MB (1)       30.6MB (2)
Drive Space for a new machine   80GB     160GB            320GB
Ratio of Drive space used       0.0195%  0.0142%          0.0093%

(1) 16   + 2 * (20*11*17/1024)
(2) 23.3 + 2 * (20*11*17/1024)

Even if you map it out to your extraordinarly large archive, we get:

                               Today    Two years        Four Years
Archive size                   300MB     307.3MB (3)     314.6MB (4)
Drive Space for a new machine   80GB     160GB            320GB
Ratio of Drive space used       0.366%   0.188%          0.096%

(3) 300   + 2 * (20*11*17/1024)
(4) 307.3 + 2 * (20*11*17/1024)

As you can see, there's no problem 

James Blackwell          Please do not send me carbon copies of mailing
Smile more!              list posts. Such mail is unsolicited. Thank you!

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