[Pulp-dev] Importers/Exporters

[David Davis]

Thanks for the responses so far. I think we could export publications along
with the repo version by exporting any publication that points to a repo
version.

My concern with exporting repositories is that users will probably get a
bunch of content they don't care about if they want to export a single repo
version. That said, if users do want to export entire repos, we could add
this feature later I think?

David


On Wed, Feb 19, 2020 at 10:30 AM Justin Sherrill <jsherril at redhat.com>
wrote:

>
> On 2/14/20 1:09 PM, David Davis wrote:
>
> Grant and I met today to discuss importers and exporters[0] and we'd like
> some feedback before we proceed with the design. To sum up this feature
> briefly: users can export a repository version from one Pulp instance and
> import it to another.
>
> # Master/Detail vs Core
>
> So one fundamental question is whether we should use a Master/Detail
> approach or just have core control the flow but call out to plugins to get
> export formats.
>
> To give some background: we currently define Exporters (ie
> FileSystemExporter) in core as Master models. Plugins extend this model
> which allows them to configure or customize the Exporter. This was
> necessary because some plugins need to export Publications (along with
> repository metadata) while other plugins who don't have Publications or
> metadata export RepositoryVersions.
>
> The other option is to have core handle the workflow. The user would call
> a core endpoint and provide a RepositoryVersion. This would work because
> for importing/exporting, you wouldn't ever use Publications because
> metadata won't be used for importing back into Pulp. If needed, core could
> provide a way for plugin writers to write custom handlers/exporters for
> content types.
>
> If we go with the second option, the question then becomes whether we
> should divorce the concept of Exporters and import/export. Or do we also
> switch Exporters from Master/Detail to core only?
>
> # Foreign Keys
>
> Content can be distributed across multiple tables (eg UpdateRecord has
> UpdateCollection, etc). In our export, we could either use primary keys
> (UUIDs) or natural keys to relate records. The former assumes that UUIDs
> are unique across Pulp instances. The safer but more complex alternative is
> to use natural keys. This would involve storing a set of fields on a record
> that would be used to identify a related record.
>
> # Incremental Exports
>
> There are two big pieces of data contained in an export: the dataset of
> Content from the database and the artifact files. An incremental export
> cuts down on the size of an export by only exporting the differences.
> However, when performing an incremental export, we could still export the
> complete dataset instead of just a set of differences
> (additions/removals/updates). This approach would be simpler and it would
> allow us to ensure that the new repo version matches the exported repo
> version exactly. It would however increase the export size but not by much
> I think--probably some number of megabytes at most.
>
> If its simper, i would go with that.  Saving even ~100-200 MB isn't that
> big of a deal IMO.  the biggest savings is in the RPM content.
>
>
>
> [0] https://pulp.plan.io/issues/6134
>
> David
>
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