[Pulp-dev] Importers/Exporters

[Justin Sherrill]

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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