Custom Eviction Policy

Question

Hello,
I am storing a few Maps into Coherence - each map might have a few hundred entries. The problem i have at this point is with the eviction policies. If i set the high units on the front map of a near cache to be 100 - it never works. It sees 1 entry per map.
I created a custom eviction policy where it will remove items from my map when the size of the map reaches the high units of that particular near cache. The problem is that this item is no longer present in the front or back map.
Is there a way to create a custom eviction policy where i can evict entries out of the front map but not the back map?
Thanks

Answer 1

When i put my maps into tangosol i just do:
NamedCache mCache = CacheFactory.getCache(cacheName);
mCache.put(cacheKey, deepCopy(cacheObj));
where cacheObject is a Map and i make a deep copy of that map for thread safety.
The map contains over 100 entries.
Here is my cache config file:
          <cache-mapping>
               <cache-name>CouponCache</cache-name>
               <scheme-name>content-near-with-eviction</scheme-name>
          </cache-mapping>
          <!--
               Near caching scheme for all Content Caches
          -->
          <near-scheme>
               <scheme-name>content-near-with-eviction</scheme-name>
               <front-scheme>
                    <local-scheme>
                         <scheme-ref>default-front-eviction</scheme-ref>
                    </local-scheme>
               </front-scheme>
               <back-scheme>
                    <distributed-scheme>
                         <backing-map-scheme>
                              <local-scheme>
                                   <scheme-ref>default-back-eviction</scheme-ref>
                              </local-scheme>
                         </backing-map-scheme>
                    </distributed-scheme>
               </back-scheme>
               <!--
                    Specifies the strategy used keep the front-tier in-sync with the back-tier
               -->
               <invalidation-strategy>present</invalidation-strategy>
               <!--
                    It specifies whether or not the cache services associated with this cache scheme should be automatically started at a cluster node.
               -->
               <autostart>true</autostart>
          </near-scheme>
          <!--
               Default front cache eviction policy scheme.
          -->
          <local-scheme>
               <scheme-name>default-front-eviction</scheme-name>
               <!--
                    Least Frequently Used eviction policy chooses which
                    entries to evict based on how often they are being
                    accessed, evicting those that are accessed least
                    frequently first. (LFU)
                    Least Recently Used eviction policy chooses which
                    entries to evict based on how recently they were
                    last accessed, evicting those that were not accessed
                    the for the longest period first. (LRU)
                    Hybrid eviction policy chooses which entries
                    to evict based the combination (weighted score)
                    of how often and recently they were accessed,
                    evicting those that are accessed least frequently
                    and were not accessed for the longest period first. (HYBRID)
               -->
               <eviction-policy>
                    <class-scheme>
                         <class-name>com.att.uma.cache.eviction.MyEvictionPolicy</class-name>
                    </class-scheme>
               </eviction-policy>
               <eviction-policy>LRU</eviction-policy>
               <!--
                    Used to limit the size of the cache.
                    Contains the maximum number of units
                    that can be placed in the cache before
                    pruning occurs.
               -->               
               <high-units>100</high-units>     
               <expiry-delay>12h</expiry-delay>
          </local-scheme>
I did not list all of the methods specified by the interface - as they are irrelevant to my issue.
Here is my eviction class:
public class MyEvictionPolicy extends AbstractMapListener implements EvictionPolicy
     private final static Log log = LogFactory.getLog(DefaultUnitCalculator.class);
     LocalCache m_cache = null;
     public MyEvictionPolicy() {}
     public void requestEviction(int cMaximum)
          int cCurrent = m_cache.getHighUnits();
          if(log.isDebugEnabled())
               log.debug("* requestEviction: current:" + cCurrent + " to:" + cMaximum);
          // eviction policy calculations
          Iterator iter1 = m_cache.entrySet().iterator();
          while(iter1.hasNext())
               Entry entry = (Entry) iter1.next();
               if (cCurrent > cMaximum)
                    if((entry.getValue() instanceof Map))
                         Map map = (Map) deepCopy(entry.getValue());
                         Iterator iter2 = ((Map) entry.getValue()).keySet().iterator();
                         while(iter2.hasNext())
                              if(cCurrent == map.size())
                                   entry.setValue(map);
                                   break;
                              String key = (String) iter2.next();
                              map.remove(key);
                              if(log.isDebugEnabled())
                                   log.debug("* requestEviction: current:" + cCurrent + " to:" + cMaximum);
               else
                    break;
}