[RFC] adding merge-node to parent lines in a commit

[RFC] adding merge-node to parent lines in a commit

[Sean]

Just a random thought presented for flamage...  Would adding the merge
node to each "parent" line in merge nodes be workable?

parent  SHA1-PARENT  SHA1-MERGE-NODE

It's not exactly clear cut I guess, especially in the case of multi-parent
merges, but it would make descending the history slightly easier.   It
would let you look at any merge, and know exactly which commits were
associated with that merge, without needing any repo-id or time
information.  This information is needed at the time of merge anyway, so
recording it rather than leaving it to be calculated later makes some
sense.  Comments?

Cheers,
Sean

Re: [RFC] adding merge-node to parent lines in a commit

[Junio C Hamano]

It is not clear to me ID of what object is being recorded as
SHA1-MERGE-NODE in your proposal.  Care to illustrate?

Re: [RFC] adding merge-node to parent lines in a commit

[Sean]

On Sun, May 15, 2005 5:30 pm, Junio C Hamano said:
> It is not clear to me ID of what object is being recorded as
> SHA1-MERGE-NODE in your proposal.  Care to illustrate?

Hey Junio,

Yes, it's pretty basic unless i'm overlooking something:

Rn---\
>    Mn
>    Mn-1
Rn-1  |
Rn-2  |
Rn-3--/
Initial

So for this particular case it's rather simple, the Rn merge node would have:

parent  Rn-1  (ommitted)
parent  Mn    Rn-3

Essentially, you are recording in the merge commit the length of each
branch that represents new commits that did not exist in this repository
before this merge.

But there are more complicated cases with multiple parent merges.   What
this would avoid is the need to calculate common_anscestor in routines
like git-rev-list, because that information would already be stored.   As
far as I know this information is already available at merge time anyway,
so recording it shouldn't be a burden.   I'm not sure it buys you a ton
out the other end, but perhaps it would be slightly easier to piece the
merge history back together.

Sean

Re: [RFC] adding merge-node to parent lines in a commit

[Junio C Hamano]

>>>>> "S" == Sean  <seanlkml@sympatico.ca> writes:

S> Yes, it's pretty basic unless i'm overlooking something:

    Rn---\
         Mn
         Mn-1
    Rn-1  |
    Rn-2  |
    Rn-3--/
    Initial

S> So for this particular case it's rather simple, the Rn merge
S> node would have:

S> parent  Rn-1  (ommitted)
S> parent  Mn    Rn-3

Isn't that something you can obtain by scanning the parents and
running merge-base across them without recording it in the
commit?

Re: [RFC] adding merge-node to parent lines in a commit

[Sean]

On Sun, May 15, 2005 6:36 pm, Junio C Hamano said:
>>>>>> "S" == Sean  <seanlkml@sympatico.ca> writes:
>
> S> Yes, it's pretty basic unless i'm overlooking something:
>
>     Rn---\
>          Mn
>          Mn-1
>     Rn-1  |
>     Rn-2  |
>     Rn-3--/
>     Initial
>
> S> So for this particular case it's rather simple, the Rn merge
> S> node would have:
>
> S> parent  Rn-1  (ommitted)
> S> parent  Mn    Rn-3
>
> Isn't that something you can obtain by scanning the parents and
> running merge-base across them without recording it in the
> commit?

Yes it is, and i was mistaken to think it gave more information.  It would
shave some time off history traversal, but nothing else.

Sean