Unexpected performance hit when switching from EmfModel to InMemoryEmfModel

[agarciadom]

Working on the TTC KMEHR to FHIR case today, I noticed that the benchmark driver in its reference solution, transforms a File into a Resource, rather than a File to a File. This is done so the "Run" phase of the measurements does not include the time used in saving the model.

To make results comparable, I decided to make the same change, and have the ETL transformation go from an EmfModel to an InMemoryEmfModel. When I did that, however, I noticed it significantly slowed down. VisualVM points to the maintenance of the allContents cache:

This wasn't an issue with EmfModel. It turns out that at some point, I added some code to register CachedContentsAdapters automatically in the initialisation of InMemoryEmfModel. I wonder why I didn't check whether caching was enabled or not at that time - I can't remember at the moment.

Later on, Sina changed the code to just use setCachingEnabled(true), which performs the same work but is also consistent with the cached flag. This is after a commit where he fixed EmfModel::setCachingEnabled to add/remove the CachedContentsAdapter itself (as it should have).

Looking at this again, I wonder if we should drop this altogether from InMemoryEmfModel, and just let users decide if they want to turn on caching or not by themselves:

  // Since 1.6, having CachedContentsAdapter implies cached=true, otherwise it's inconsistent.
  setCachingEnabled(true);

[arcanefoam]

I think the user should always decide. If not, users will see/perceive the performance/memory hit and be confused if they are not selecting the cached option.

[kolovos]

So is the issue that caching is disabled by default for instances of EmfModel but enabled by default for instances of InMemoryEmfModel?

[agarciadom]

Actually, it might be better to just drop the allContents cache - I don't see how it improves performance in most scenarios, as we would normally be traversing the whole model anyway.

[agarciadom]

So is the issue that caching is disabled by default for instances of EmfModel but enabled by default for instances of InMemoryEmfModel?

We may reduce the impact of this default by dropping the allContents cache, yes, but it's still an inconsistency anyway. At the very least, we should document this default.

[kolovos]

I think I'd set the default value of expand to true in AbstractEmfModel for consistency.