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Language:
English
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Language:
English
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Chapter 9. Other Considerations for Translator Development
9.1. Caching API
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.
Note
In special circumstances where the translator has performed its own caching, it can indicate to the engine that the results should not be cached or reused by setting the
Scope
to Scope.NONE
.
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.
Note
If you plan on modifying the
CacheDirective
during execution, return a new instance from the ExecutionFactory.getCacheDirective
call, rather than returning a shared instance.
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.
option
|
default
|
---|---|
scope
|
Session
|
ttl
|
rs cache ttl
|
readAll
|
true
|
updatable
|
true
|
prefersMemory
|
false
|