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Re: [equinox-dev] Convergence between p2 and the OSGiresolver+repository

Hi guys,

Some documents about the way the SAT encoding works are available here:
https://hal.archives-ouvertes.fr/hal-00870855/document

and here:
http://dev.eclipse.org/mhonarc/lists/p2-dev/pdf7BeCW3Xx01.pdf

If you are willing to give a try to a SAT encoding of uses, I am happy to give a hand.

Cheers,

Daniel

Le 17/11/2016 à 22:41, Thomas Watson a écrit :
I will be interested to see if you can successfully map the OSGi uses
concept into the SAT solver p2 uses.  I briefly looked at that a long
time ago when we were refactoring the Equinox framework (Luna) and were
replacing the old Equinox resolver.  It was far from obvious how you
would achieve this.  At that time I opt'ed to collaborate with a common
resolver in Felix for the Equinox framework.  But this is no magic
implementation.  There are still cases where the OSGi resolver algorithm
will blow up.  In Equinox we try to minimize that possibility by
avoiding the resolution of all (10000) bundles at once.  But as Pascal
states, this does leave out some possible valid solutions that you will
then not discover while resolving.

If you do focus on how to map uses into the SAT solver in p2 I would be
interested in collaborating to see if such a resolver would outperform
the Felix resolver we use at runtime.  My hope at the time I was looking
into this was to map an OSGi Resolver service on top of the SAT solver
implementation.  But I cannot remember how the SAT solver is driven.  I
suspect the split between the OSGI Resovler and the OSGi ResolveContext
will not fit well into the SAT implementation model.

Tom





From:        Todor Boev <rinsvind@xxxxxxxxx>
To:        Equinox development mailing list <equinox-dev@xxxxxxxxxxx>
Date:        11/17/2016 02:22 AM
Subject:        Re: [equinox-dev] Convergence between p2 and the OSGi
     resolver+repository
Sent by:        equinox-dev-bounces@xxxxxxxxxxx
------------------------------------------------------------------------



- Regarding batch resolution:
Ultimately I think the batch processing is about performance. At
provisioning time where finding the best solution trumps speed the
resolver can be executed against the entire set. But I have to try this.
After than the equinox runtime should be able to re-create a correct
(maybe not identical) resolution from the much smaller set of resources.
I have tried the resolver against about 700 bundles and it did okay, but
this is well short of 10,000. More research required....some day.

- Regarding the additional p2 concepts:
Can you point me to the documentation of how the resolution problem is
converted to a SAT formula?

Best regards

On Thu, Nov 17, 2016 at 6:20 AM, Pascal Rapicault
<_pascal@xxxxxxxxxxxxxx <mailto:pascal@xxxxxxxxxxxxx>> wrote:
On 11/16/2016 10:49 AM, Todor Boev wrote:
- Regarding resolver behavior:
  The goal is actually to replace the behavior of the objective function
with the behavior of the resolver. This is the best way to guarantee
that both p2 and the OSGi runtime agree on what is a consistent set of
bundles. For example p2 does not take into account package uses
constraints which leads to p2 selecting bundles that later fail to
resolve at runtime. It does not matter which way to resolve is better,
so long as they agree. Since the OSGi resolver is very unlikely to
change it falls on p2 to match it's behavior. My current company
(software ag) has had quite a number of issues where essentially p2 sets
up the resolver to fail.

- Regarding resolver scalability:
  The resolution is split between the resolver which processes the
current set of resources and the resolver context which selects
candidates when asked. If the goal is to support a very high number of
candidates - a resolver context impl optimized for searches in a large
candidate space can be provided. If the goal is to produce a solution
that includes a very high number of resources - more research is
required. Even if the initial set is 10,000 the resolver can be asked to
process them not all at once, but incrementally in batches or even one
by one. Which is in fact what equinox does today.
    The thing is that if you look at a subset of the available bundles,
you may find a solution that is not the optimal one. p2 will consider
all the possible candidates in one resolution invocation.


I am trying to determine if it makes sense to invest effort in prototyping this given that subtle changes in behavior are in fact a goal, rather than an issue. Even though on the surface p2 resolver looks similar to what the OSGi resolver does, p2 has at least 2 additional concepts: 1) the expression of strict negation 2) the concept of patch

I'm tempted to think that it is probably simpler to add support for the
uses-clause in p2 (this has been a known issue for years, but I can't
seem to find the bug tonight) than it is to replace the resolver
completely and get all the tests to pass. The encoding of dependencies
to a SAT formula is well documented and so are the optimization functions.


On Wed, Nov 16, 2016 at 4:44 AM, Pascal Rapicault <_pascal@xxxxxxxxxxxxxx <mailto:pascal@xxxxxxxxxxxxx>> wrote: On 11/15/2016 12:52 PM, Todor Boev wrote: Hello,

Are there any plans to bring together p2 and OSGi resolver+repository
standards?
    There is no immediate plan for this.

It should be beneficial to have similar (maybe identical?) dependency
resolution at provisioning time and later at runtime.
    The install time and runtime resolvers resolve a slightly different
problem because the install time resolver has to look for candidates in
a large space, whereas the runtime one has to connect as many components
together.
    I have not tried replacing the p2 resolver with the new OSGi
resolver so I can't tell how it would perform.


Specifically: - Is it possible to publish the bundle generic capabilities/requirements to the p2 repository? Yes this should be possible. The underlying p2 capability / requirement model is really extensible and the current limitation is only the serialized format.

- Is it possible to use the equinox Resolver inside the p2 Planner?
    It is possible to get something going but I'm not sure if this will
scale (p2 resolver is able to perform seamlessly on 10's of thousands of
IUs), nor if you will be able to replicate the subtleties that result
from having an objective function.

-  Even if the equinox Resolver can not be used is it possible for p2 to
handle generic requirements/capabilities?
    Yes. This should not be too much work.



Regards,
Todor Boev


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