Combining changests considered harmfull? (Re: hg: hsx/hsx16/baseline: 6893095: G1: bulk G1 backports to hs16)

[Volker Simonis]

Hi Tony,

referring to your last change I just wanted to raise the question if
there's a general policy in place with regard to combined changesets
and if combined changesets should be considered harmful?

I understand that combining several changesets into one big changeset
as you did may considerably simplify the integration of changes from
one repository into another one. But at which prize?

If somebody is looking at the bug description of 6888619, he won't be
able to see that 6888619 is fixed in hsx16. He won't even see that
6888619 is related to 6893095, although the fix for 6888619 is a part
of the fix for 6893095. Even if somebody is just browsing hsx16, he
won't see at a first glance that 6888619 was fixed in hsx16, because
until now, the convention is that the bug ID is the first word of a
change description, but in the case of 6893095, the bug ID of 6888619
only appears in the summary field the description for 6893095.

I already noticed this kind of slackness in hsx14.1 when the fixes for
the three bugs 6786503, 6787254 and 6821507 where submitted as a
single changeset for 6786503. This is of course worse, because here
there isn't even an umbrella changesets which describes which other
changeset it contains.

In general I would strongly vote against such mixing and combination
of changesets from one repository into others even if this comes at
the prize of a bigger merge overhead because it makes tracking of
changes extremely difficult. I think Mercurial offers enough
possibilities for the task of transferring changesets from one
repository into another even if the repositories aren't related (e.g.
import/export or  transplant
(http://mercurial.selenic.com/wiki/TransplantExtension)).

What do you think? Has this issue been discussed previously?

Regards,
Volker

On 10/21/09, antonios.printezis at sun.com <antonios.printezis at sun.com> wrote:
> Changeset: 6de2c9c36168
>  Author:    tonyp
>  Date:      2009-10-20 19:55 -0400
>  URL:       http://hg.openjdk.java.net/hsx/hsx16/baseline/rev/6de2c9c36168
>
>  6893095: G1: bulk G1 backports to hs16
>  Summary: Backports of CRs 6888619, 6888316, 6847956, 6882730, 6885041, 6887186, and 6861557.
>  Reviewed-by: never, ysr, johnc, jmasa, apetrusenko, iveresov
>
>  ! src/cpu/sparc/vm/c1_LIRGenerator_sparc.cpp
>  ! src/share/vm/gc_implementation/g1/concurrentG1Refine.cpp
>  ! src/share/vm/gc_implementation/g1/concurrentG1Refine.hpp
>  ! src/share/vm/gc_implementation/g1/concurrentG1RefineThread.cpp
>  ! src/share/vm/gc_implementation/g1/concurrentG1RefineThread.hpp
>  ! src/share/vm/gc_implementation/g1/concurrentMark.cpp
>  ! src/share/vm/gc_implementation/g1/concurrentMark.hpp
>  ! src/share/vm/gc_implementation/g1/concurrentMarkThread.cpp
>  ! src/share/vm/gc_implementation/g1/concurrentMarkThread.hpp
>  ! src/share/vm/gc_implementation/g1/concurrentZFThread.cpp
>  ! src/share/vm/gc_implementation/g1/concurrentZFThread.hpp
>  ! src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp
>  ! src/share/vm/gc_implementation/g1/heapRegion.cpp
>  ! src/share/vm/gc_implementation/g1/heapRegion.hpp
>  ! src/share/vm/gc_implementation/g1/heapRegionSeq.cpp
>
>