Stream: implementers
Topic: If-Unmodified-Since
Johannes Höhn (Jul 30 2019 at 09:24):
The Managing Resource Contention section in the http chapter describes the If-Match header as a solution for Optimistic concurrency control. However this only works if the Server understands versioning. The HTTP standard also offers the If-Unmodified-Since header for cases where the Last-Modified Header is known. Is there any precedent in using it for FHIR?
Grahame Grieve (Jul 30 2019 at 09:56):
I don’t recall discussing it before - that doesn’t mean that you can’t use it, just that we haven’t talked about it
Alexander Kiel (Jul 30 2019 at 16:52):
As HTTP dates have only second resolution and depends on proper clock sync, the use of an If-Unmodified-Since header will not provide 100% certainty to not override an already done update. If you can live with that restriction, the next question would be whether FHIR server will support that header.
Grahame Grieve (Jul 30 2019 at 19:41):
mine doesn't.
Johannes Höhn (Jul 31 2019 at 07:11):
You don't need clock sync as you use the last-modified header or meta.lastUpdated, but you're right that it's a problem if a resource gets updated more than once per second.
Alexander Kiel (Jul 31 2019 at 07:16):
@Johannes Höhn Yes you are right, you can use the value from the last-modified header like a weak ETag with second resolution.
Joe Lamy (Apr 19 2021 at 18:50):
https://jira.hl7.org/browse/FHIR-31927
Last updated: Apr 12 2022 at 19:14 UTC
