bug#20137: number of generation doesn't always rise monotonically

bug#20137: number of generation doesn't always rise monotonically

[Tomáš Čech]

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Generation number is not always the maximum of all generation numbers
and so generation number is not always monotonic.

Steps to reproduce:

Lets start with on generation N.

1] install some package (you'll have N and N+1)
2] install some other package (you'll have N, N+1 and N+2)
3] delete generation N+1 (you'll have N and N+2)
4] switch to generation N
5] install some package - you'll get generation N+1 again
   (you'll have N, N+1 and N+2 again)

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bug#20137: number of generation doesn't always rise monotonically

[Ludovic Courtès]

Tomáš Čech <sleep_walker@gnu.org> skribis:

> 1] install some package (you'll have N and N+1)
> 2] install some other package (you'll have N, N+1 and N+2)
> 3] delete generation N+1 (you'll have N and N+2)
> 4] switch to generation N
> 5] install some package - you'll get generation N+1 again
>   (you'll have N, N+1 and N+2 again)

That’s expected, yes.  What makes you think it’s a problem?

When implementing that, there were several possible choices:

  1. Upon rollback to N, remove all generations above N.  Rejected
     because it gratuitously prevents useful use cases.

  2. Upon rollback from P to N, keep all the generations, but use P+1
     for the next generation number.  Doesn’t work, because rolling back
     from P+1 would bring you back to P instead of N.

  3. The current behavior.

See <http://lists.gnu.org/archive/html/bug-guix/2013-01/msg00325.html>
for part of the discussion.

Thanks,
Ludo’.

bug#20137: number of generation doesn't always rise monotonically

[Taylan Ulrich Bayırlı/Kammer]

ludo@gnu.org (Ludovic Courtès) writes:

>   2. Upon rollback from P to N, keep all the generations, but use P+1
>      for the next generation number.  Doesn’t work, because rolling back
>      from P+1 would bring you back to P instead of N.

Perhaps we can eventually move to an actual tree structure where the
nodes can be named whatever.  Until now I thought that's how generations
work, and are just named after integers for identification purposes.

Taylan

bug#20137: number of generation doesn't always rise monotonically

[Thompson, David]

On Wed, Mar 18, 2015 at 4:47 PM, Taylan Ulrich Bayırlı/Kammer
<taylanbayirli@gmail.com> wrote:
> ludo@gnu.org (Ludovic Courtès) writes:
>
>>   2. Upon rollback from P to N, keep all the generations, but use P+1
>>      for the next generation number.  Doesn’t work, because rolling back
>>      from P+1 would bring you back to P instead of N.
>
> Perhaps we can eventually move to an actual tree structure where the
> nodes can be named whatever.

+1

- Dave

bug#20137: number of generation doesn't always rise monotonically

[Ludovic Courtès]

taylanbayirli@gmail.com (Taylan Ulrich "Bayırlı/Kammer") skribis:

> ludo@gnu.org (Ludovic Courtès) writes:
>
>>   2. Upon rollback from P to N, keep all the generations, but use P+1
>>      for the next generation number.  Doesn’t work, because rolling back
>>      from P+1 would bring you back to P instead of N.
>
> Perhaps we can eventually move to an actual tree structure where the
> nodes can be named whatever.

I agree this would be the right thing for a real undo mechanism.

But how useful would it be?  I’ve never been in a situation where
rollback/switch-generation would be insufficient or inappropriate.

I’m concerned that this would add both code and user interface
complexity for mostly hypothetical use cases.  WDYT?

Thanks,
Ludo’.

bug#20137: number of generation doesn't always rise monotonically

[Ludovic Courtès]

tag 20137 notabug
thanks

I think the initial “bug” report can be closed.  Feel free to open
another bug or wishlist item if you think something must be done in this
area.

Thanks to both of you!

Ludo’.

bug#20137: number of generation doesn't always rise monotonically

[Tomáš Čech]

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Sorry, for some reason I didn't get any e-mail and noticed only
closing the bug. I'll subscribe to bug-guix ML to prevent it.


> That’s expected, yes.  What makes you think it’s a problem?

First, it was conflicting experience with what you were saying on IRC.
User experience was a bit confusing because the behaviour seemed
unexpected.

>When implementing that, there were several possible choices:
>
>  1. Upon rollback to N, remove all generations above N.  Rejected
>       because it gratuitously prevents useful use cases.
>
>  2. Upon rollback from P to N, keep all the generations, but use P+1
>     for the next generation number.  Doesn’t work, because rolling back
>     from P+1 would bring you back to P instead of N.

I can't understand this reason. It doesn't look like valid reason to
me, but only consequence of current implementation. It seems that you
don't store information about what was the previous generation and
that is whole point.

>  3. The current behavior.
>
>See <http://lists.gnu.org/archive/html/bug-guix/2013-01/msg00325.html>
>for part of the discussion.

Thanks for looking that up!



>Perhaps we can eventually move to an actual tree structure where the
>nodes can be named whatever.  Until now I thought that's how generations
>work, and are just named after integers for identification purposes.

Yes, I had this in mind as well.


>I agree this would be the right thing for a real undo mechanism.

Exactly!

>But how useful would it be?  I’ve never been in a situation where
>rollback/switch-generation would be insufficient or inappropriate.

I haven't met such situation either (yet).

>I’m concerned that this would add both code and user interface
>complexity for mostly hypothetical use cases.  WDYT?

Yes, it would surely add some more code and would be demanding for
creating good visual represantation for users, but it could also be
much closer to behavior user would expect. And that is something which
makes tools to be natural to use.

Thank you all for your comments.

S_W

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bug#20137: number of generation doesn't always rise monotonically

[Ludovic Courtès]

Tomáš Čech <tcech@suse.cz> skribis:

>>Perhaps we can eventually move to an actual tree structure where the
>>nodes can be named whatever.  Until now I thought that's how generations
>>work, and are just named after integers for identification purposes.

[...]

>>I’m concerned that this would add both code and user interface
>>complexity for mostly hypothetical use cases.  WDYT?
>
> Yes, it would surely add some more code and would be demanding for
> creating good visual represantation for users, but it could also be
> much closer to behavior user would expect. And that is something which
> makes tools to be natural to use.

I’m not sure.  My guess is that an undo-style tree would turn out to be
less obvious or more difficult to use.

Currently, understanding what’s going on with M-x guix-generations or
--list-generations and similar is fairly straightforward.

Thanks for your feedback,
Ludo’.

bug#20137: number of generation doesn't always rise monotonically

[Tomáš Čech]

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On Mon, Mar 23, 2015 at 10:13:13AM +0100, Ludovic Courtès wrote:
>Tomáš Čech <tcech@suse.cz> skribis:
>
>>>Perhaps we can eventually move to an actual tree structure where the
>>>nodes can be named whatever.  Until now I thought that's how generations
>>>work, and are just named after integers for identification purposes.
>
>[...]
>
>>>I’m concerned that this would add both code and user interface
>>>complexity for mostly hypothetical use cases.  WDYT?
>>
>> Yes, it would surely add some more code and would be demanding for
>> creating good visual represantation for users, but it could also be
>> much closer to behavior user would expect. And that is something which
>> makes tools to be natural to use.
>
>I’m not sure.  My guess is that an undo-style tree would turn out to be
>less obvious or more difficult to use.
>
>Currently, understanding what’s going on with M-x guix-generations or
>--list-generations and similar is fairly straightforward.

I'm not using emacs for controling guix at all. But I should start - I can see
that is completely different user experience!

Thanks!

S_W

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