Unable to get refresh-ahead functionality working

Question

We are attempting to implement a cache with a refresh ahead so that the calling code never experience any latency due to a synchronous load from the cache loader that happens if requesting an object that has expired (so just standard refresh ahead as documented). I can't seem to get the configuration to recognize the refresh ahead setting at all - it behaves the same way regardless of whether or not the <refresh-ahead-factor> setting is included, and never does an asynchronous load. All the other settings in the configuration work as expected. I have included the configuration and what I expect the behaviour to be and what it currently is.
Is there anything else in other configuration files, etc that needs to set up to enable asynchronous loads via the refresh-ahead-factor? Note I have tried upping the worker threads via the thread-count in tangosol-coherence-override.xml (no difference).
One thing I couldn't seem to find in the documents is when the asynchronous load will occur. I assume it is near real time after a triggering 'get' after the refresh-ahead-factor, but if not that could explain the behaviour. Is there some setting that controls this, or does it happen as soon as a worker thread gets to it?
In my tests I am running a single cluster node on my local machine (version 3.3 Grid Edition in Development mode). Note the 20second expiry and .5 refresh-ahead factor is just for test purposes to see behaviour, in production it will be 12hours with a higher refresh factor such as .75.
Current behaviour (appears to be standard read-through and ignore the refresh-ahead-factor):
- request for an object that does not exist in cache blocks the calling code until it is loaded and put into the cahce via the cache loader
- request for an object that exists before the exiry period has passed (before 20 seconds since load in this configuration) since it was loaded returns the object from cache.
- request for an object that exists after the exiry period has passed (after 20 seconds since load in this configuration) blocks the calling code until it is loaded and put into the cahce via the cache loader.
- No requests ever appear to trigger asynchronous loads via the cache loader
Expected behaviour, given the .5 refresh-ahead-factor
- request for an object that does not exist in cache blocks the calling code until it is loaded and put into the cahce via the cache loader (same as above)
- request for an object that exists before the exiry period has passed (before 20 seconds since load in this configuration) since it was loaded returns the object from cache, and triggers an asynchronous reload of the object via the cache loader if requested after the refresh ahead factor. So in this example I would expect that if I requested an object out of the cache between 10 - 20 seconds after it was loaded, it would return it from cache immediately and trigger an asynchronous reload of this object via the cache loader.
- request for an object that exists in cache but has not been requested during the 10-20second period blocks the calling code until it is loaded and put into the cahce via the cache loader.
Here is the entry from our coherence-cache-config.xml
<distributed-scheme>
<scheme-name>rankedcategories-cache-all-scheme</scheme-name>
<service-name>DistributedCache</service-name>
<backing-map-scheme>
<read-write-backing-map-scheme>
<scheme-name>rankedcategoriesLoaderScheme</scheme-name>
<internal-cache-scheme>
<local-scheme>
<scheme-ref>rankedcategories-eviction</scheme-ref>
</local-scheme>
</internal-cache-scheme>
<cachestore-scheme>
<class-scheme>
<class-name>com.abe.cache.coherence.rankedcategories.RankedCategoryCacheLoader</class-name>
</class-scheme>
</cachestore-scheme>
<refresh-ahead-factor>.5</refresh-ahead-factor>
</read-write-backing-map-scheme>
</backing-map-scheme>
<autostart>true</autostart>
</distributed-scheme>
<local-scheme>
<scheme-name>rankedcategories-eviction</scheme-name>
<expiry-delay>20s</expiry-delay>
</local-scheme>

Answer 1

Hi Leonid,
Yes, it works as expected. refresh-ahead works approximately like this :
public Object get(Object oKey) {
Entry entry = getEntry();
if (entry != null and entry is about to expire) {
schedule refresh();
return entry.getValue();
If you want to reload infrequently accessed entries you can do something like this (obviously this will not work if cache is size limited) :
<?xml version="1.0"?>
<!DOCTYPE cache-config SYSTEM "cache-config.dtd">
<cache-config>
    <caching-scheme-mapping>
        <cache-mapping>
            <cache-name>fdg*</cache-name>
            <scheme-name>fdg-cache-all-scheme</scheme-name>
        </cache-mapping>
    </caching-scheme-mapping>
    <caching-schemes>
        <distributed-scheme>
            <scheme-name>fdg-cache-all-scheme</scheme-name>
            <service-name>DistributedCache</service-name>
            <backing-map-scheme>
                <!--
                Read-write-backing-map caching scheme.
                -->
                <read-write-backing-map-scheme>
                    <scheme-name>categoriesLoaderScheme</scheme-name>
                    <internal-cache-scheme>
                        <local-scheme>
                            <expiry-delay>10s</expiry-delay>
                            <flush-delay>2s</flush-delay>
                            <listener>
                                    <class-scheme>
                                        <class-name>com.sgcib.fundingplatform.coherence.ReloadListener</class-name>
                                        <init-params>
                                            <init-param>
                                                <param-type>string</param-type>
                                                <param-value>{cache-name}</param-value>
                                            </init-param>
                                            <init-param>
                                                <param-type>com.tangosol.net.BackingMapManagerContext</param-type>
                                                <param-value>{manager-context}</param-value>
                                            </init-param>
                                        </init-params>
                                    </class-scheme>
                            </listener>
                        </local-scheme>
                    </internal-cache-scheme>
                    <cachestore-scheme>
                        <class-scheme>
                            <class-name>com.sgcib.fundingplatform.coherence.DBCacheStore</class-name>
                        </class-scheme>
                    </cachestore-scheme>
                    <refresh-ahead-factor>0.5</refresh-ahead-factor>
                </read-write-backing-map-scheme>
            </backing-map-scheme>
            <autostart>true</autostart>
        </distributed-scheme>
        <local-scheme>
            <scheme-name>categories-eviction</scheme-name>
            <expiry-delay>10s</expiry-delay>
            <flush-delay>2s</flush-delay>
        </local-scheme>
    </caching-schemes>
</cache-config>
package com.sgcib.fundingplatform.coherence;
import com.tangosol.net.BackingMapManagerContext;
import com.tangosol.net.DefaultConfigurableCacheFactory;
import com.tangosol.net.cache.CacheEvent;
import com.tangosol.util.MapEvent;
import com.tangosol.util.MultiplexingMapListener;
import java.util.Map;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadFactory;
* dimitri Nov 26, 2008
public class ReloadListener extends MultiplexingMapListener
    String                                  m_sCacheName;
    DefaultConfigurableCacheFactory.Manager m_bmmManager;
    ExecutorService m_executorService = Executors.newSingleThreadExecutor(new ThreadFactory()
    public Thread newThread(Runnable runnable)
        Thread thread = new Thread(runnable);
        thread.setDaemon(true);
        return thread;
    public ReloadListener(String sCacheName, BackingMapManagerContext ctx)
        m_sCacheName = sCacheName;
        m_bmmManager =
            (DefaultConfigurableCacheFactory.Manager) ctx.getManager();
    protected void onMapEvent(MapEvent evt)
        if (evt.getId() == MapEvent.ENTRY_DELETED && ((CacheEvent) evt).isSynthetic())
            m_executorService.execute(
                new ReloadRequest(m_bmmManager.getBackingMap(m_sCacheName), evt.getKey()));
    public void finalize()
        m_executorService.shutdownNow();
    class ReloadRequest implements Runnable
        Map    m_map;
        Object m_oKey;
        public ReloadRequest(Map map, Object oKey)
            m_map  = map;
            m_oKey = oKey;
        public void run()
            m_map.get(m_oKey);
package com.sgcib.fundingplatform.coherence;
import java.util.Collection;
import java.util.Map;
import java.util.Date;
import com.tangosol.net.cache.CacheStore;
import com.tangosol.net.CacheFactory;
import com.tangosol.net.NamedCache;
import com.tangosol.util.Base;
public class DBCacheStore extends Base implements CacheStore
     * Return the value associated with the specified key, or null if the
     * key does not have an associated value in the underlying store.
     * @param oKey key whose associated value is to be returned
     * @return the value associated with the specified key, or
     *         null if no value is available for that key
    public Object load(Object key)
        CacheFactory.log("load(" + key + ") invoked on " + Thread.currentThread().getName(),
            CacheFactory.LOG_DEBUG);
        return new Date().toString();
     * Return the values associated with each the specified keys in the
     * passed collection. If a key does not have an associated value in
     * the underlying store, then the return map will not have an entry
     * for that key.
     * @param colKeys a collection of keys to load
     * @return a Map of keys to associated values for the specified keys
    public Map loadAll(Collection colKeys)
        throw new UnsupportedOperationException();
    public void erase(Object arg0)
// TODO Auto-generated method stub
    public void eraseAll(Collection arg0)
// TODO Auto-generated method stub
    public void store(Object arg0, Object arg1)
// TODO Auto-generated method stub
    public void storeAll(Map arg0)
// TODO Auto-generated method stub
    // Test harness
    public static void main(String[] asArg)
        try
            NamedCache cache = CacheFactory.getCache("fdg-test");
            cache.get("bar"); // this will not be requested and reloaded by the
                              // listener
            while (true)
                CacheFactory.log("foo= " + cache.get("foo"), CacheFactory.LOG_DEBUG);
                Thread.sleep(1000l);
        catch (Throwable oops)
            err(oops);
        finally
            CacheFactory.shutdown();
    }Regards,
Dimitri