New VCS CachingMapper implementation using ehcache

To activate the cache, it must be added in the default-repository-config.xml that is used (usually from a template): <cachingMapper enabled="true" class="org.nuxeo.ecm.core.storage.sql.UnifiedCachingMapper"> <property name="ehcacheFilePath">/opt/vcs-ehcache.xml</property> </cachingMapper> Then an Ehcache configuration file (/opt/vcs-ehcache.xml in the example) must be provided. There are two possible examples for this file (see ticket comments): one for XA, which provides the same transaction isolation semantics as the default cache (READ COMMITTED), one without XA, which provides a transaction isolation of READ UNCOMMITTED but is faster. In any case the Ehcache configuration must be tuned the expected or measured usage, especially sizing and disk spill off. When starting with this cache the logs contain: INFO [UnifiedCachingRowMapper] Creating ehcache manager for VCS, using ehcache file: /opt/vcs-ehcache.xml This cache can be monitored using JMX, under the root "net.sf.ehcache".