Smile CDR v2024.05.PRE
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18.4.1Caching

 

The FHIR Gateway includes a cache which can be used to avoid duplicate calls to the target servers when repeated identical invocations are made to the gateway in short succession, and in some cases can be used to buffer subsequent pages of search results.

To enable the cache, set the Pagination Cache Provider to either CAFFEINE (for a local in-memory cache), or INFINISPAN (for a remote networked cache). To disable the cache, a value of NONE can be used (this is the default).

This cache currently has the following properties, and it may be enhanced in the future:

  • FHIR Search (including subsequent page requests), FHIR Read/VRead operations, and FHIR Operation invocations are cached. No other actions are cached.
  • Caches are user-specific. In other words, if the same user performs the same search twice in a row, they may get a cached result. If a different user performs the same search, they will not get a cached result.
  • Caching happens before any security services are applied, meaning that consent services or authorization services will be applied to results every time.

18.4.1.1Buffering Search Results

In some cases, an enabled cache may also be used to buffer pages of search results.

As a simple example, suppose a client is performing a search against a FHIR Gateway using a route that matches 2 target servers. The client might specifically request pages of 10 results using a _count=10 parameter on the search URL. The FHIR Gateway will in turn ask each target server to provide search results satisfying this search.

If each target server returns 5 results, then all results will be returned immediately. However, if each server returns 10 results, then only the first target's results will actually be returned to the server. The remaining 10 results will be placed in the cache, and returned from cache when the client requests the next page of results. If the cache is disabled, then the FHIR Gateway will need to repeat the search a second time.

18.4.1.2Detecting Cache Hits

When performing a FHIR Search or a FHIR Read operation, the client response from the gateway will include a header called X-Cache, which will contain a value starting with HIT if the operation results were fetched from the cache as opposed to being fetched from the target server.

In the case of searches which aggregate data from multiple targets, a request is considered a cache hit only if all target responses were served from the cache.