Should the <shared-cache-mode> element in a persistence unit definition automatically turn on the data cache?
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                 Key: OPENJPA-1532
                 URL: https://issues.apache.org/jira/browse/OPENJPA-1532
             Project: OpenJPA
          Issue Type: Question
          Components: datacache
    Affects Versions: 2.0.0-beta, 2.0.0-M3, 2.0.0-M2, 2.0.0-M1, 2.0.0, 2.0.1, 2.1.0
            Reporter: Jody Grassel
            Priority: Minor


The JPA 2.0 spec introduces a new persistence unit definition element, <shared-cache-mode>, which accepts NONE, ALL, ENABLE_SELECTIVE, and DISABLE_SELECTIVE.  The JPA 2.0 spec section 3.7.1 documents the behavior of each of those modes.

What I am curious about is if the use of <shared-cache-mode> should implicitly enable OpenJPA's data cache plugin.  Currently, the above element is completely ignored if the persistence unit is missing the properties: openjpa.DataCache=true and openjpa.RemoteCommitProvider=sjvm (because by default, OpenJPA disables data caching).  My interpretation of the spec suggests that <shared-cache-mode> is not only a platform-independent method of instructing the data cache which entities are eligible for admittance to the data cache, but it is also a switch providing a platform-independent method of both turning the data cache on or off (since whether the cache is enabled by default is platform-specific).  Otherwise, why have a NONE value, if it was not intended to be a platform independent means of turning the data cache off?

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