Large memory usage

[derosm2]

Taking a look at memory usage using, I was able to see that fhir_stu3_models comes in at 31 MiB (for comparison Rails is at 28 MiB).

Specifically I was using https://github.com/schneems/derailed_benchmarks and running bundle exec derailed bundle:mem

bundle exec derailed bundle:mem
TOP: 175.75 MiB
  fhir_client: 77.7852 MiB
    fhir_stu3_models: 31.3828 MiB
        lib/fhir_stu3_models/fhir/resources/ImagingStudy.rb: 5.3008 MiB
        lib/fhir_stu3_models/fhir/resources/DocumentManifest.rb: 1.9961 MiB
        lib/fhir_stu3_models/fhir/resources/DocumentReference.rb: 1.9023 MiB
        lib/fhir_stu3_models/fhir/resources/AuditEvent.rb: 1.6875 MiB
        lib/fhir_stu3_models/fhir/resources/Procedure.rb: 1.375 MiB
        lib/fhir_stu3_models/fhir/resources/CarePlan.rb: 1.0586 MiB
        lib/fhir_stu3_models/fhir/resources/Observation.rb: 0.9844 MiB
        lib/fhir_stu3_models/fhir/resources/FamilyMemberHistory.rb: 0.9219 MiB
        lib/fhir_stu3_models/fhir/resources/Condition.rb: 0.8867 MiB
        lib/fhir_stu3_models/fhir/resources/PlanDefinition.rb: 0.7305 MiB
        lib/fhir_stu3_models/fhir/resources/Media.rb: 0.7031 MiB
        lib/fhir_stu3_models/fhir/resources/Patient.rb: 0.625 MiB
        lib/fhir_stu3_models/fhir/resources/ProcedureRequest.rb: 0.5781 MiB
        lib/fhir_stu3_models/fhir/resources/MedicationStatement.rb: 0.5391 MiB
        lib/fhir_stu3_models/fhir/resources/AllergyIntolerance.rb: 0.5273 MiB
        lib/fhir_stu3_models/fhir/resources/ExplanationOfBenefit.rb: 0.5156 MiB
        lib/fhir_stu3_models/fhir/resources/TestScript.rb: 0.5039 MiB
        lib/fhir_stu3_models/fhir/resources/MedicationRequest.rb: 0.4688 MiB
        lib/fhir_stu3_models/fhir/resources/Questionnaire.rb: 0.4648 MiB
        lib/fhir_stu3_models/fhir/resources/Substance.rb: 0.4336 MiB
        lib/fhir_stu3_models/fhir/resources/Specimen.rb: 0.3398 MiB
        lib/fhir_stu3_models/fhir/resources/CapabilityStatement.rb: 0.3242 MiB
        lib/fhir_stu3_models/fhir/resources/DeviceUseStatement.rb: 0.3242 MiB
        lib/fhir_stu3_models/fhir/resources/CareTeam.rb: 0.3086 MiB

This issue gets exacerbated because we are not just including fhir_stu3_models. We use fhir_client which also needs fhir_dstu2_models and fhir_models (which brings the total up to 77 MiB).

Further details can be examined by running bundle exec derailed bundle:objects. Largely seems to be an issue with string allocations due to how the models are defined.

I'm not sure what the right solution to this problem is, but I think it's worth noting so that others can be aware of the memory footprint required by these gems.