Re: Configuration Management for Ada on Unix

[pautet@email.enst.fr (Laurent Pautet)]

Theodore E. Dennison <dennison@escmail.orl.mmc.com> wrote:
>Laurent Pautet wrote:
>> Maybe I am wrong, but I think SCCS is very unefficient because it
>> stores patches between Version (N+1) - Version (N) and when you want
>> to access to version N, internally SCCS retrieves version 0 and
>> applies all the patches to obtain version N. RCS stores the last
>> version (rather than the first one) and differences between Version
>> (N) - Version (N+1).
>> 
>
>That depends on what you mean by "inefficient". Assuming you aren't
>making massive changes to files when you check them out, it is very
>efficient for disk space, at the expense of checkout and checkin 
>time.

No, no. What I mean is to get the last version of a file, SCCS gets
the first version and applies all the patches to get the last
version. With RCS or CVS, the last version is always there. To get the
previous version, RCS applies a patch. My argument concerns the way
the storage space is structured. SCCS and RCS have different storage
models, different ways of building a given version. SCCS starts from
the first version, RCS starts from the last version. That's all. The
storage size is the same but the time to build the last version is
(N-1) * T for SCCS and 0 for RCS (T = average time to apply a patch, N
= number of file version). It is the difference between SCCS's
interleaved deltas and RCS's reverse deltas. Retrieving the last
version is a very common operation. So, RCS is more time efficient
than SCCS. Concerning disk space, it is almost exactly the same
efficiency based on difference between two successive versions.
-- 
-- Laurent