Grant and I met today to discuss importers and exporters 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.  https://pulp.plan.io/issues/6134 David
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