How to avoid the absences of the Cache?

Hello


Before I explain the problem, it's my current setup.

-Partitioned/distributed cache
-JPA annotated classes
-Support card linked to an oracle database
-Objects are stored in the POF format
-C++ extend clients

When I ask something that does not exist in the cache, the JPA magic forms a query and assembles the object and which stores in the cache.

However if the query returns no results so consistent returns a lack of cache. Our hierarchy of existing objects may request items that do not exist (this infrastructure is vast and entrenched and changing, it's not an option). This blows near the performance of cache out of the water.

What I want to do is to intercept a lack of cache and store a null object in the cache on this key (null, it will be 4 bytes of length). Client code can interpret the null as a lack of cache object and everything will work as usual - however the null object is stored in the cache and close performance will return.

My problem is, as the JPA annotated done any 'magic', I do not get to intercept if the query returns an empty set. I tried both triggers of card and listeners, but as expected they don't called as no result set is generated.

Does anyone know of a port of entry where I can return an object to consistency in the case of a query that returns an empty set. I also want the option to configure this behavior on a per-cache basis.

Any help gratefully received.

Thank you
Rich

Published by: Rich Carless on January 6, 2011 13:56

Hello

If you use 3.6 you can do so by writing a subclass of JpaCacheStore that implements BinaryEntryStore or way more genric (that would be for other people who have asked similar questions recently) would be to write an implementation of BinaryEntryStore that wraps another cache store.

Here's one that I hit until recently...

package org.gridman.coherence.cachestore;

import com.tangosol.net.BackingMapManagerContext;
import com.tangosol.net.CacheFactory;
import com.tangosol.net.DefaultConfigurableCacheFactory;
import com.tangosol.net.cache.BinaryEntryStore;
import com.tangosol.net.cache.CacheStore;
import com.tangosol.run.xml.XmlElement;
import com.tangosol.util.Binary;
import com.tangosol.util.BinaryEntry;

import java.util.Set;

public class WrapperBinaryCacheStore implements BinaryEntryStore {

    private BackingMapManagerContext context;

    private CacheStore wrapped;

    public WrapperBinaryCacheStore(BackingMapManagerContext context, ClassLoader loader, String cacheName, XmlElement cacheStoreConfig) {
        this.context = context;
        DefaultConfigurableCacheFactory cacheFactory = (DefaultConfigurableCacheFactory) CacheFactory.getConfigurableCacheFactory();
        DefaultConfigurableCacheFactory.CacheInfo info = cacheFactory.findSchemeMapping(cacheName);
        XmlElement xmlConfig = cacheStoreConfig.getSafeElement("class-scheme");
        wrapped = (CacheStore)cacheFactory.instantiateAny(info, xmlConfig, context, loader);
    }

    @Override
    public void erase(BinaryEntry binaryEntry) {
        wrapped.erase(binaryEntry.getKey());
    }

    @SuppressWarnings({"unchecked"})
    @Override
    public void eraseAll(Set entries) {
        for (BinaryEntry entry : (Set)entries) {
            erase(entry);
        }
    }

    @Override
    public void load(BinaryEntry binaryEntry) {
        Object value = wrapped.load(binaryEntry.getKey());
        binaryEntry.updateBinaryValue((Binary) context.getValueToInternalConverter().convert(value));
    }

    @SuppressWarnings({"unchecked"})
    @Override
    public void loadAll(Set entries) {
        for (BinaryEntry entry : (Set)entries) {
            load(entry);
        }
    }

    @Override
    public void store(BinaryEntry binaryEntry) {
        wrapped.store(binaryEntry.getKey(), binaryEntry.getValue());
    }

    @SuppressWarnings({"unchecked"})
    @Override
    public void storeAll(Set entries) {
        for (BinaryEntry entry : (Set)entries) {
            store(entry);
        }
    }

}

You re like this using the JPA example in the tutorial of 3.6 consistency of...


    jpa-distributed
    JpaDistributedCache
    
        
            
                
            
            
                
                    org.gridman.coherence.cachestore.WrapperBinaryCacheStore
                    
                        
                            com.tangosol.net.BackingMapManagerContext
                            {manager-context}
                        
                        
                            java.lang.ClassLoader
                            {class-loader}
                        
                        
                            java.lang.String
                            {cache-name}
                        
                        
                            com.tangosol.run.xml.XmlElement
                            
                                
                                    com.tangosol.coherence.jpa.JpaCacheStore
                                    
                                        
                                            java.lang.String
                                            {cache-name}
                                        
                                        
                                            java.lang.String
                                            com.oracle.handson.{cache-name}
                                        
                                        
                                            java.lang.String
                                            JPA
                                        
                                    
                                
                            
                        
                    
                
            
        
    
    true

As you can see it the WrapperBinaryCacheStore takes four parameters cpnstructor (configured in the settings-init)

  • First is the card holder frame
  • Second is the ClassLoader
  • Third is the name of cache
  • Fourth is the XML configuration for the cache store that you want to encapsulate

    If the load method of the wrapped store cache returns null (i.e. nothing in DB corresponds to the key), then instead of returning null, the BinaryEntry is updated with a binary file that represents the null value. Because the corresponding key is now in the cache with a null value, then the cache store is not recalled for the same key.

    Note If you do this, and then later your DB is updated with the values for the keys Traoré were previously null (by something other than consistency) then coherence does not charge them because he is never going to charge for these keys.

    I gave the above code a quick test and it seems to work fine.

    If you are using 3.5 then you can still do it but you must use the coherence incubator common library that has a version of BinaryCacheStore. The code and configuration will be similar but not identical.

    JK

    Edited by: Jonathan.Knight January 6, 2011 15:50

    • Tags: Fusion Middleware

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