Chapter 9. Other Considerations for Translator Development

Translators may contribute cache entries to the result set cache by the use of the CacheDirective object. Translators wishing to participate in caching should return a CacheDirective from the ExecutionFactory.getCacheDirective method, which is called prior to execution. The commands passed to getCacheDirective will have already been vetted to ensure that the results are eligible for caching. For example update commands or commands with pushed dependent sets will not be eligible for caching.

If the translator returns null for the CacheDirective , which is the default implementation, the engine will not cache the translator results beyond the current command. It is up to your custom translator or custom delegating translator to implement your desired caching policy.

The returned CacheDirective will be set on the ExecutionContext and is available via the ExecutionContext.getCacheDirective() method. Having ExeuctionFactory.getCacheDirective called prior to execution allows the translator to potentially be selective about which results to even attempt to cache. Since there is a resource overhead with creating and storing the cached results it may not be desirable to attempt to cache all results if it is possible to return large results that have a low usage factor. If you are unsure about whether to cache a particular command result you may return an initial CacheDirective then change the Scope to Scope.NONE at any time prior to the final cache entry being created and the engine will give up creating the entry and release its resources.

The CacheDirective readAll Boolean field is used to control whether the entire result should be read if not all of the results were consumed by the engine. If readAll is false then any partial usage of the result will not result in it being added as a cache entry. Partial use is determined after any implicit or explicit limit has been applied. The other fields on the CacheDirective object map to the cache hint options . See the table below for the default values for all options.