Re: [Gnu-arch-users] libraries / cacherevs

[Aaron Bentley]

On Thu, 2004-02-26 at 09:53, Johannes Berg wrote:
> This item falls into the "What would tla do?" category ;-)
> 
> I just wanted to check out the moinmoin archive, and since its unsigned
> I got messages about everything tla was looking for in my library.
> Now, moin has 250 patches in the current branch. tla went all the way
> back through 2 branches to find that nothing about that was in my
> library, only to then find that the archive had a cacherev at patch-194.

In order to do its hard-linking, library-add reimplements part of
build-revision.  Library-add desperately wants to find a revision it can
hard-link from, so it will seek as far back as it can.

The backbuild--1 will do the same, but it currently uses unsafe
optomizations.  It will skip from c--patch-254 to c--base-0 to
b--patch--123 to b--base-0 to a--patch--30 to a--base-0.  This radically
reduces the amount of time it takes to seek backwards.

The then will look forwards in that version, to see if there's a
suitable more-recent library.

> I don't know what would have happened if I had had patch-10 in my
> library, would tla have patched from patch-10 or from the cacherev at
> patch-194?

Library.  For library-add, library revisions trump all other kinds,
because of the hard-link thing.

For a non-library get, the 50 revisions rule will select the cacherev.

> In any case, I'm interested in what it would have done 
> a) plain tla
> b) the changes with reverse-building etc
> 
> because I really think it should use patch-194 :-)

For libraries, it's a time/space decision that tla isn't really
qualified to make.
Unknown factors:
- which files have changed since patch-10?
- how long will it take to apply the difference between patch-10 and
patch-194?
- how much do you value your space?

To allow the import to be used, we'd need a way of re-linking files that
had not changed between patch-10 and patch-190.  Pretty much the same
idea as "tla changes --link".

Aaron
-- 
Aaron Bentley
Director of Technology
PanoMetrics, Inc.