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Re: [p2-dev] Planner explanation question

What is returned by the slicer is not an explanation, but just a "bunch of notes" collected along the way as it was slicing. The information collected is very vague and here is an example why. I have the following IUs
A requires B [0, 3.0)
B-1 requires C 
B-1.1 requires E
B-2 requires D
D
When the slicer is slicing for A, it will include B-1, B-1.1 and B-2  in the slice. Now when it slices B-1 it will fail at finding a C and will create a log. Same will go for B-1.1 with E. When it comes to B-2 it will find D. In this case, the resolution of A will have a solution. Now if I take B-2 out of the set of available IUs, then the slicer will return 2 warnings but really only one of those warnings would have to be "fixed" for a solution to be found. Of course this is a small example, if you follow all the possibilities of all the versions you can get a lot of noise from which it may be hard for you to figure out what is really missing.

Computing an explanation is done by the core SAT solver and will sort through the noise to figure out something that you can act upon.
I will let Daniel explain if more can actually be done.

I have released the test you provided, but it is not enabled as part of the global test suite.

PaScaL

On 2011-05-12, at 2:45 PM, Todorova, Katya wrote:

The Slicer returns all missing requirements properly but if there's an attempt to calculate the minimal explanation, some of these reqirements are cut off and only the first one is returned to the end user.
 
Here's the part of code that calculates the explanation:
 
if (s.getCode() != UNSATISFIABLE || (context != null && !(context.getProperty(EXPLANATION) == null || Boolean.TRUE.toString().equalsIgnoreCase(context.getProperty(EXPLANATION))))) {
    ...

    return plan;                          //that plan status contains all problematic requirements though all substatus codes are "Warning"

}


//Extract the explanation

Set<Explanation> explanation = projector.getExplanation(sub.newChild(ExpandWork / 4));     //here some of missing requirements are removed and the only one remaining is marked as Error.

Test case attached.
 
What is the minimal explanation supposed to contain?
 
Thanks,
Katya

From: p2-dev-bounces@xxxxxxxxxxx [mailto:p2-dev-bounces@xxxxxxxxxxx] On Behalf Of Pascal Rapicault
Sent: Thursday, May 12, 2011 8:56 PM
To: P2 developer discussions
Subject: Re: [p2-dev] Planner explanation question

From a quick code inspection to SimplePlanner, setting explanation to false will completely disable the explanation support (this is used in the case of the dropins to avoid computing the explanation since there is no one to read it).
Some of the missing requirements are filtered as part of the Slicer (but this is expected and filter out the noise), but after that the explanation is constructed by the solver and it tries to return the minimal explanation between what you have installed and what you are trying to install.

However if you have several missing requirements I think it will stop at the first one. Is that the pb you are seeing?

If you can provide an automated test case, we could see what can be done.

On 2011-05-12, at 1:40 PM, Todorova, Katya wrote:

Hi guys,
 
I came across a strange behavior of p2 planner - it hides information when trying to resolve an IU and resolution fails (due to missing requirements for example).
If there are more than one missing requirements the final explanation (and corresponding MultiStatus) will contain only the first one found. This default behavior
could be avoided if "org.eclipse.equinox.p2.director.explain" property is set to "false" in the provisioning context used by the planner.
 
I thought that the explanation is supposed to contain more details than the "ordinary" status but it turned out it's not the case and it contains even less. Is that expected?
If yes, any idea why?
 
Thanks in advance,
Katya
 
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