[Pulp-dev] Changesets Challenges

[Dennis Kliban]

On Fri, Apr 6, 2018 at 10:15 AM, Brian Bouterse <bbouters at redhat.com> wrote:

> Several plugins have started using the Changesets including pulp_ansible,
> pulp_python, pulp_file, and perhaps others. The Changesets provide several
> distinct points of value which are great, but there are two challenges I
> want to bring up. I want to focus only on the problem statements first.
>
> 1. There is redundant "differencing" code in all plugins. The Changeset
> interface requires the plugin writer to determine what units need to be
> added and those to be removed. This requires all plugin writers to write
> the same non-trivial differencing code over and over. For example, you can
> see the same non-trivial differencing code present in pulp_ansible
> <https://github.com/pulp/pulp_ansible/blob/d0eb9d125f9a6cdc82e2807bcad38749967a1245/pulp_ansible/app/tasks/synchronizing.py#L217-L306>,
> pulp_file
> <https://github.com/pulp/pulp_file/blob/30afa7cce667b57d8fe66d5fc1fe87fd77029210/pulp_file/app/tasks/synchronizing.py#L114-L193>,
> and pulp_python
> <https://github.com/pulp/pulp_python/blob/066d33990e64b5781c8419b96acaf2acf1982324/pulp_python/app/tasks/sync.py#L172-L223>.
> Line-wise, this "differencing" code makes up a large portion (maybe 50%) of
> the sync code itself in each plugin.
>
>
That is definitely a problem. We should address this.


> 2. Plugins can't do end-to-end stream processing. The Changesets
> themselves do stream processing, but when you call into
> changeset.apply_and_drain() you have to have fully parsed the metadata
> already. Currently when fetching all metadata from Galaxy, pulp_ansible
> takes about 380 seconds (6+ min). This means that the actual Changeset
> content downloading starts 380 seconds later than it could. At the heart of
> the problem, the fetching+parsing of the metadata is not part of the stream
> processing.
>
>
This is the same problem we currently have in Pulp 2. We should address
this.


> Do you see the same challenges I do? Are these the right problem
> statements? I think with clear problem statements a solution will be easy
> to see and agree on.
>
>
Yes, I do. You described the problems very well.


> Thanks!
> Brian
>
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