[Pulp-dev] uniqueness constraints within a repository version

Brian Bouterse bbouters at redhat.com
Wed Jul 24 20:01:54 UTC 2019

On Mon, Jul 22, 2019 at 4:47 AM Tatiana Tereshchenko <ttereshc at redhat.com>

> On Sun, Jul 21, 2019 at 3:00 PM Brian Bouterse <bbouters at redhat.com>
> wrote:
>> On Sun, Jul 21, 2019 at 6:23 AM Tatiana Tereshchenko <ttereshc at redhat.com>
>> wrote:
>>> +1 to the idea of a repo_key.
>>> Should we also add the ability to apply custom validation of the content
>>> being added?
>>> Similar to a repo_key, Content model can optionally provide an
>>> additional validator.
>>> Use cases:
>>>  - for pulp_file to avoid relative path overlap - e.g. 'a/b' and 'a'
>> In thinking this over more, I'm unsure that pulp_file has the use case.
>> Two different Artifacts having relative paths 'a' and 'a/b' in one repo
>> version doesn't seem problematic. This problem statement is similar to the
>> Distribution.base_path overlap problem statement where it's unavoidably
>> ambiguous which Distribution should be matched when base_paths are allowed
>> to overlap. In this case for pulp_file, it's not ambiguous in the same way,
>> the relative_path I expect to match to exactly 1 content unit either 'a',
>> or 'a/b', but not both. What do you think about this?
> I agree that the problem is similar to the Distribution.base_path overlap.
> If I understand you correctly, yes, it's not a problem if you query content
> one by one.
> What about use cases when we want to have a repo version on a filesystem?
> E.g. Browsable repositoiries (this feature has already been asked for by
> our stakeholders), export (e.g. rsync).
I see now that the exporting to a filesystem use case make any repo
containing units 'a' and 'a/b' because 'a' can't be both a directory and a
file on POSIX filesystems. We should identify this requirement in our
plugin docs somehow.

I was thinking webservers themselves are in the same situation. They have
to store content on disk, but they also have to serve 'a' and 'a/b' to the
user. To make this work they have 'a' actually serve up index.html. In
practice the binary data served at 'a' isn't stored at 'a' on the
filesystem but actually 'a/index.html' or 'a/index.txt' or something. The
data you would serve up as a directory's response would be an index of the
directory so this makes logical sense to me also. At export time one option
is to translate 'a' to 'a/index.html' which in terms of having webservers
serving it back up is kind of necessary. What do you think?

If ^ is what we do then the overlapping 'a' and 'a/b' I think would be ok
again. What do you think about this?

>>  - for pulp_rpm to filter by signature/signing key
>> Can we expand on this use case a bit? Is it that the repo version should
>> only contains units signed or unsigned rpms? Or is it that we are ok with a
>> mixture as long as each NEVRA is unique? I suspect the former, but I want
>> to be sure.
> I think it should contain only signed units and optionally signed by
> specific keys only. See pulp 2 feature description
> https://docs.pulpproject.org/plugins/pulp_rpm/user-guide/features.html#package-signatures-and-gpg-key-id-filtering
> Another use case which comes to mind is: keeping the last N versions of a
> unit within a repo verison.
I agree w/ this use case. In the context of repo_key, I don't see a
relationship between the repo_key mechanism for preserving repo-level
uniqueness and how it would also resolve this. Did you have an idea that
could handle all of these cases with one mechanism?

> Tanya
>>> Plugins can solve it by defining their own stage but it seems like
>>> almost any plugin needs to ensure absence of collisions specific to it,
>>> even the simple pulp_file.
>>> It means that our default pipeline becomes less useful and will be
>>> hardly ever used by any [currently known] plugins.
>>> Any thoughts?
>>> Tanya
>>> On Mon, Jul 8, 2019 at 9:09 PM Brian Bouterse <bbouters at redhat.com>
>>> wrote:
>>>> I want to retell Simon's proposal to have "Content defines a 'repo_key'
>>>> similar to a unit_key. This key must be unique within a repo version (and
>>>> not globally like the unit_key."
>>>> We could adopt his proposal to have the repo_key tuple defined on
>>>> Content in pulpcore. If we left the add/remove APIs in core and adopt for
>>>> both sync and add/remove a "keep newest to associate" functionality
>>>> described earlier in the thread. This "keep newest to associate" code would
>>>> be used by sync in the form of a core stage that is a generalized version
>>>> of the RemoveDuplicates stage. This would become part of the default
>>>> pipeline for all users of Stages API. I think this would be better than
>>>> plugin writers implementing it over and over and also less effort for
>>>> plugin wrtiers. This design would meet the current needs of pulp_cookbook,
>>>> pulp_file, and pulp_rpm which are the only 3 places I know we have this
>>>> problem so far, but I believe more content types are susceptible to this.
>>>> What do you think we should do?
>>>> Thanks!
>>>> Brian
>>>> On Thu, Jun 27, 2019 at 4:03 AM Tatiana Tereshchenko <
>>>> ttereshc at redhat.com> wrote:
>>>>> Sure, the code can be de-duplicated.
>>>>> My main worry is that it's a responsibility of a plugin writer not to
>>>>> forget to ensure uniqueness constraints within a repo version for every
>>>>> workflow (sync, copy, anything else) where a repo version is created.
>>>>> Every time before RepositoryVersion.create() is called, there should
>>>>> be a check that there is no colliding content in a repo version.
>>>>> It would be much more reliable and friendly, in my opinion, if plugin
>>>>> writer could define rules/callbacks/whatever for each content and it would
>>>>> be applied to any repository creation.
>>>>> At the same time this eliminates the flexibility to define different
>>>>> logic for content collision for different workflows, however I'm not sure
>>>>> if such a use case exists or is desired.
>>>>> Tanya
>>>>> On Wed, Jun 26, 2019 at 6:49 PM Austin Macdonald <amacdona at redhat.com>
>>>>> wrote:
>>>>>> @Tanya Tereshchenko <ttereshc at redhat.com>
>>>>>>> Do I understand correctly that it doesn't cover the sync case and
>>>>>>> it's only about explicit repo version creation?
>>>>>> I don't mean that add/remove could not share code with remove
>>>>>> duplicate stage. I wanted to point out that we have a problem here (how to
>>>>>> remove duplicates) that has similar patterns to other problems with add
>>>>>> remove (recursive, copy, deciding which content to keep with a collision,
>>>>>> etc.) I don't doubt that pulpcore could help solve these problems, but I
>>>>>> think that as we approach our GA, we should consider solving this problem
>>>>>> (for now) by getting out of the way of plugin writers rather than by
>>>>>> implementing code that is supposed to work for all plugins. I suspect that
>>>>>> plenty of the plugins will be implementing their own add/remove anyway.
>>>>>> On Tue, Jun 25, 2019 at 12:56 PM David Davis <daviddavis at redhat.com>
>>>>>> wrote:
>>>>>>> I don't think this solution would work in the case of creating a new
>>>>>>> repository version. Suppose for example you had two content units that
>>>>>>> collide, one in a repo version and one older unit that a user explicitly
>>>>>>> wants to add to the repo version. If the latter one is older, then what
>>>>>>> would happen?
>>>>>>> David
>>>>>>> On Tue, Jun 25, 2019 at 12:48 PM Brian Bouterse <bbouters at redhat.com>
>>>>>>> wrote:
>>>>>>>> Having a way for units to express their uniqueness per repo sounds
>>>>>>>> good because then more areas of Pulp's code could answer the question:
>>>>>>>> "will I have a duplicate if I add content X to repo_version Y".
>>>>>>>> Let's assume we know that situation is about to occur during sync
>>>>>>>> for example, what do we do about it? In the errata case we know the "new"
>>>>>>>> one should replace the existing one. Maybe we start to 'order' the units
>>>>>>>> with colliding repo keys and keep the newest one always? Would this work
>>>>>>>> for pulp_cookbook and pulp_rpm? Would it generalize? Is this what you
>>>>>>>> imagined?
>>>>>>>> On Tue, Jun 25, 2019 at 5:30 AM Tatiana Tereshchenko <
>>>>>>>> ttereshc at redhat.com> wrote:
>>>>>>>>> Do I understand correctly that it doesn't cover the sync case and
>>>>>>>>> it's only about explicit repo version creation?
>>>>>>>>> So the suggestion is to implement the same logic twice: for sync
>>>>>>>>> case - RemoveDuplicates stage and/or maybe some custom stage (e.g. to
>>>>>>>>> disallow overlapping paths), and for direct repo version creation - your
>>>>>>>>> proposal.
>>>>>>>>> On Mon, Jun 24, 2019 at 3:13 PM Austin Macdonald <
>>>>>>>>> amacdona at redhat.com> wrote:
>>>>>>>>>> I have a design in mind for solving this problem:
>>>>>>>>>> 1. Remove POST to RepositoryVersion (no general add/remove
>>>>>>>>>> endpoint).
>>>>>>>>>> 2. Add an endpoint to kick off an add/remove task, namespaced by
>>>>>>>>>> plugin. ie `POST pulp/api/v3/docker/add-remove/`
>>>>>>>>>>    This view can be provided to all plugins by the plugin
>>>>>>>>>> template, and will be based on the current RepositoryVersionCreate:
>>>>>>>>>> https://github.com/pulp/pulpcore/blob/master/pulpcore/app/viewsets/repository.py#L221-L258
>>>>>>>>>>    Note: the main purpose of this view is to kick off the general
>>>>>>>>>> add/remove task, which will be unchanged:
>>>>>>>>>> https://github.com/pulp/pulpcore/blob/master/pulpcore/app/tasks/repository.py#L70
>>>>>>>>>> 3. Add an add/remove serializer to the plugin API.
>>>>>>>>>> 3. Plugins needing further customization can provide their own
>>>>>>>>>> task and subclassed serializer.
>>>>>>>>>> This gives the plugin writer full control over the endpoint
>>>>>>>>>> (customizable arguments and validation), and full control over the flow
>>>>>>>>>> (extra logic, depsolving, enforced uniqueness). It only uses the existing
>>>>>>>>>> patterns (and existing required knowledge), but requires no work (other
>>>>>>>>>> than using the template) for the simple case.
>>>>>>>>>> On Mon, Jun 3, 2019 at 2:56 PM Simon Baatz <gmbnomis at gmail.com>
>>>>>>>>>> wrote:
>>>>>>>>>>> On Mon, Jun 03, 2019 at 09:11:07AM -0400, David Davis wrote:
>>>>>>>>>>> >    @Simon I like the idea behind the repo_key solution you
>>>>>>>>>>> came up with.
>>>>>>>>>>> >    Can you be more specific around cases you think that it
>>>>>>>>>>> couldn't
>>>>>>>>>>> >    handle? I imagine that plugin writers could use properties
>>>>>>>>>>> or
>>>>>>>>>>> >    denormailzation (ie additional database columns) to solve
>>>>>>>>>>> cases where
>>>>>>>>>>> >    they need uniqueness across data that isn't in the
>>>>>>>>>>> database. In a worst
>>>>>>>>>>> >    case scenario, they can't use the pulpcore solution and
>>>>>>>>>>> just have to
>>>>>>>>>>> >    roll their own.
>>>>>>>>>>> What I wrote probably sounded too pessimistic. You are right, in
>>>>>>>>>>> most cases that should be doable.
>>>>>>>>>>> I agree that we could have a simple default solution that just
>>>>>>>>>>> requires to specify a couple of field names in the easiest
>>>>>>>>>>> case.  As you
>>>>>>>>>>> say, it should be possible use custom logic in a plugin if
>>>>>>>>>>> required.
>>>>>>>>>>> Here is the case I was thinking of that it can't handle:
>>>>>>>>>>> In pulp_file, a uniqueness constraint on "relative_path" would
>>>>>>>>>>> allow
>>>>>>>>>>> content units "a" and "a/b" to be in a repo version.
>>>>>>>>>>> However, we may want file repos to be representable on an actual
>>>>>>>>>>> file
>>>>>>>>>>> system (e.g. when exporting them as tar files).  For the repo
>>>>>>>>>>> above,
>>>>>>>>>>> this does not work, as "a" can't be a file and a directory at the
>>>>>>>>>>> same time on a standard Unix file system.
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