Hazelcast Near Cache not working with simple example

Question

I'm currently using hazelcast version 3.9

I have tried several ways to implement Near cache and it seems I am not able to find the correct way. Below I have share my code and let me know exactly where I am going wrong.

    public class NearCacheExample {

    public static void main(String[] args) throws IOException 
    {
        HazelcastConfig hzConfig = new HazelcastConfig();

        HazelcastInstance hzInstance = hzConfig.getHZInstance();

        IMap<Double, String> nearCacheMap = hzInstance.getMap("cacheExample");

        for (int i = 0; i < 100000; i++) {
            nearCacheMap.set(Math.random(), i + "");
        }

        long startTime = System.currentTimeMillis();

        System.out.println("---------------------------Before Sort----------------------------------");

        for (Entry<Double, String> entrySet : nearCacheMap.entrySet()) {

            Double key = entrySet.getKey();
            String value = entrySet.getValue();

        }

        long endTime = System.currentTimeMillis();

        System.out.println("------------------------------------------------Read Both---------------------------------------------------");

        NearCacheStats nearCacheStatistics = nearCacheMap.getLocalMapStats().getNearCacheStats();

        System.out.println( "Near Cache hit/miss ratio 3= "
                + nearCacheStatistics.getHits());

        System.out.println("Near cache implemented or not " + nearCacheMap.getLocalMapStats().getNearCacheStats().getOwnedEntryCount());

        System.out.println(" EndTime timeDifference : " + startTime + " " + endTime + " " +(endTime-startTime));

    }
}

The output I am getting while I check for NearCache stats is completely 0.

HazelcastConfig.java file

public class HazelcastConfig 
{

    public HazelcastInstance getHZInstance() throws IOException
    {
        ClientConfig cfg = new XmlClientConfigBuilder("src/main/resources/hazelcast-client.xml").build();

        return HazelcastClient.newHazelcastClient(cfg);
    }
}

Configuration at Hazelcast client

<near-cache name="default">
<in-memory-format>BINARY</in-memory-format>
<invalidate-on-change>true</invalidate-on-change>
<eviction eviction-policy="NONE" max-size-policy="ENTRY_COUNT" size="10"/>

I have also tried changing cache name inside hazelcast-client.xml file. Nothing seems to work

On the hazelcast server side there is no changes.

Answer 1

@Tatkal

1. map.set invalidates the near cache put don't put the new value there
2. Near Cache only used for key-based access, your loop doesn't hit Near Cache at all. You need to change second line in the loop like this : String value = nearCacheMap.get(entrySet.getKey()); or change the loop to keySet like

        for (Double key : nearCacheMap.keySet()) {
            String value = entrySet.getValue(key);
        }

3. Even after change, you'll still see 0 since you only did 1 get operation, and it was a cache miss. If you repeat loop & stats print multiple times, you'll see this:

---------------------------Before Sort----------------------------------
------------------------------------------------Read Both---------------------------------------------------
Near Cache hit/miss ratio = 0 / 100000
Near cache implemented or not 10
 EndTime timeDifference : 1548313357643 1548313362527 4884
------------------------------------------------Read Both---------------------------------------------------
Near Cache hit/miss ratio = 10 / 199990
Near cache implemented or not 10
 EndTime timeDifference : 1548313357643 1548313367155 9512
------------------------------------------------Read Both---------------------------------------------------
Near Cache hit/miss ratio = 20 / 299980
Near cache implemented or not 10
 EndTime timeDifference : 1548313357643 1548313371688 14045