Question

我使用Cassandra作为持久存储以及Hazelcast 3.6。用于休息API（POST）。 Mapstore实现如下所示。

import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ExecutionException;

import com.datastax.driver.core.Cluster;
import com.datastax.driver.core.ResultSet;
import com.datastax.driver.core.ResultSetFuture;
import com.datastax.driver.core.Row;
import com.datastax.driver.core.Session;
import com.datastax.driver.core.querybuilder.Insert;
import com.datastax.driver.core.querybuilder.QueryBuilder;
import com.hazelcast.core.MapStore;

public class InventoryMapStoreImpl implements MapStore<String, Map<String, Integer>> {

    public static Cluster cluster;
    public static Session session;

    public InventoryMapStoreImpl() {
        cluster = Cluster.builder().addContactPoint("127.0.0.1").build();
        session = cluster.connect("company");
    }

    @Override
    public synchronized Map<String, Integer>  load(String key) {

        Map<String, Integer> qty = new HashMap<String, Integer>();
        ResultSetFuture futureList = session
                .executeAsync("Select * from company.onhandinventoryavailability WHERE key='" + key + "';");
        try {

            if (futureList.get() != null) {
                ResultSet rsFuture = futureList.get();
                Row resultOne = rsFuture.one();
                if (resultOne != null) {
                    qty = resultOne.getMap(1, String.class, Integer.class);
                }
            }
            session.close();
            cluster.close();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
        return qty;
    }

    @Override
    public Map<String, Map<String, Integer>> loadAll(Collection<String> keys) {
        return null;
    }

    @Override
    public Iterable<String> loadAllKeys() {
        return null;
    }

    @Override
    public synchronized void store(String key, Map<String, Integer> value) {

        try {

            Insert insert = QueryBuilder.insertInto("onhandinventoryavailability")
                    .value("key", key);
              insert.value("value", value);
              session.execute(insert);
            System.out.println("INSERTED:"+key+" INTO CASSANDRA...");
        } catch (Exception e) {
            System.out.println("ERORRRR");
            e.printStackTrace();
        }
        session.close();
        cluster.close();
    }

    @Override
    public void storeAll(Map<String, Map<String, Integer>> map) {
    }

    @Override
    public void delete(String key) {
    }

    @Override
    public void deleteAll(Collection<String> keys) {
    }
}

地图的hazelcast xml条目是。

map name="onHandInventoryAvailability">
                <map-store enabled="true">
                        <class-name>com.company.common.hazelcast.mapstore.InventoryMapStoreImpl</class-name>
                        <write-delay-seconds>5</write-delay-seconds>
                        <write-batch-size>1000</write-batch-size>
                        <write-coalescing>true</write-coalescing>
                </map-store>
                <in-memory-format>BINARY</in-memory-format>
                <backup-count>1</backup-count>
                <async-backup-count>0</async-backup-count>
                <time-to-live-seconds>0</time-to-live-seconds>
                <max-idle-seconds>0</max-idle-seconds>
                <eviction-policy>NONE</eviction-policy>
                <max-size policy="PER_NODE">0</max-size>
                <eviction-percentage>25</eviction-percentage>
                <min-eviction-check-millis>100</min-eviction-check-millis>
                <merge-policy>com.hazelcast.map.merge.PutIfAbsentMapMergePolicy</merge-policy>
                <cache-deserialized-values>INDEX-ONLY</cache-deserialized-values>
         </map>

问题在于，当我在延迟或一次一个地点击POST api后，数据同时出现在hazelcast和cassandra中，但是当我做更多的POST表示10,100等时，与cassandra的连接被hazelcast和写入丢失了后面没有正常工作。只有10,100等中的一两个记录去cassandra（不是全部）。我的mapstore实现有什么问题吗？

Answer 1

Hazelcast只会实例化您的MapStore实施，并在此实例上调用load，store等方法。这意味着您只需连接一个Cassandra群集并打开一个会话（在MapStore的构造函数中），并且只调用一次load或store方法时，断开与Cassandra集群的连接。这解释了代码的当前行为。

Cassandra司机的Cluster＆amp; Session个对象应该跨越应用程序的整个生命周期[1]。正如评论中已经建议的那样，在应用程序关闭之前，不应该关闭它们。

[1] http://docs.datastax.com/en/developer/java-driver/2.0/java-driver/fourSimpleRules.html

Hazelcast使用Cassandra写下来

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