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Getting Member Statistics

You can get various statistics from your distributed data structures via the Statistics API. Since the data structures are distributed in the cluster, the Statistics API provides statistics for the local portion (1/Number of Members in the Cluster) of data on each member.

Map Statistics

To get local map statistics, use the getLocalMapStats() method from the IMap interface. This method returns a LocalMapStats object that holds local map statistics.

Below is an example code where the getLocalMapStats() method and the getOwnedEntryCount() method get the number of entries owned by this member.

        HazelcastInstance hazelcastInstance = Hazelcast.newHazelcastInstance();
        IMap<String, String> customers = hazelcastInstance.getMap( "customers" );
        LocalMapStats mapStatistics = customers.getLocalMapStats();
        System.out.println( "number of entries owned on this member = "
                + mapStatistics.getOwnedEntryCount() );
Since Hazelcast IMDG 3.8 getOwnedEntryMemoryCost() method is now supported for NATIVE in-memory format as well.

The following are some of the metrics that you can access via the LocalMapStats object:

  • Number of entries owned by the member (getOwnedEntryCount()).

  • Number of backup entries held by the member (getBackupEntryCount()).

  • Number of backups per entry (getBackupCount()).

  • Memory cost (number of bytes) of owned entries in the member (getOwnedEntryMemoryCost()).

  • Creation time of the map on the member (getCreationTime()).

  • Number of hits (reads) of the locally owned entries (getHits()).

  • Number of get and put operations on the map (getPutOperationCount() and getGetOperationCount()).

  • Number of queries executed on the map (getQueryCount() and getIndexedQueryCount()) (it may be imprecise for queries involving partition predicates (PartitionPredicate) on the off-heap storage).

See the LocalMapStats Javadoc to see all the metrics.

Map Index Statistics

To access map index statistics, if you are using indexes to speed up map queries, use the getIndexStats() method of the LocalMapStats interface returned by IMap.getLocalMapStats().

Below is an example where the getIndexStats() method is used to examine an average selectivity of index hits:

        HazelcastInstance hazelcastInstance = Hazelcast.newHazelcastInstance();
        IMap<String, String> customers = hazelcastInstance.getMap("customers");
        addIndex(customers, "name", true); // or add the index using the map config
        LocalMapStats mapStatistics = customers.getLocalMapStats();
        Map<String, LocalIndexStats> indexStats = mapStatistics.getIndexStats();
        LocalIndexStats nameIndexStats = indexStats.get("name");
        System.out.println("average name index hit selectivity on this member = "
                + nameIndexStats.getAverageHitSelectivity());

The following are some of the metrics that you can obtain via the LocalIndexStats interface:

  • Number of queries and hits into an index (getQueryCount() and getHitCount()): Number of hits and queries may differ since a single query may hit the same index more than once.

  • Average index hit latency measured in nanoseconds (getAverageHitLatency())

  • Average index hit selectivity (getAverageHitSelectivity): Returned values are in the range from 0.0 to 1.0. Values close to 1.0 indicate a high selectivity meaning the index is efficient; values close to 0.0 indicate a low selectivity meaning the index efficiency is approaching an efficiency of a simple full scan.

  • Number of index insert, update and remove operations (getInsertCount(), getUpdateCount() and getRemoveCount()).

  • Total latencies of insert, update and remove operations (getTotalInsertLatency(), getTotalUpdateLatency(), getTotalRemoveLatency()): To compute an average latency divide the returned value by the number of operations of a corresponding type.

  • Memory cost of an index (getMemoryCost()): For on-heap storages, this memory cost metric value is a best-effort approximation and doesn’t indicate a precise on-heap memory usage of an index.

See the LocalIndexStats Javadoc to see all the metrics.

To compute an aggregated value of getAverageHitSelectivity() for all cluster members, you can use a simple averaging computation as shown below:

(s(1) + s(2) + ... + s(n)) / n

In this computation, s(i) is an average hit selectivity on the member i and n is the total number of cluster members.

A more advanced solution is to compute a weighted average as shown below:

(s(1) * h(1) + s(2) * h(2) + ... + s(n) * h(n)) / (h(1) + h(2) + ... + h(n))

Here, s(i) is an average hit selectivity on the member i, h(i) is a hit count (getHitCount()) on the member i and n is the total number of cluster members. This more advanced solution may produce more precise results in unstable dynamic clusters where new members do not have enough statistics accumulated. The same technique may be applied to the getAverageHitLatency() metric.

Accuracy and reliability notes:

  • For on-heap storage, values returned by getAverageHitSelectivity() may be 1% more or less than the actual selectivity. For example, if the actual selectivity is 0.9, the returned value could be between 0.89 and 0.91.

  • The values returned by getQueryCount() and getHitCount() may be imprecise for queries involving partition predicates (PartitionPredicate) on off-heap storage.

  • The index statistics may be imprecise after a new cluster member addition or the existing member removal until enough fresh statistics is accumulated on a new owner of an index or its partition.

Near Cache Statistics

To get Near Cache statistics, use the getNearCacheStats() method from the LocalMapStats object. This method returns a NearCacheStats object that holds Near Cache statistics.

Below is an example code where the getNearCacheStats() method and the getRatio method from NearCacheStats get a Near Cache hit/miss ratio.

        HazelcastInstance hazelcastInstance = Hazelcast.newHazelcastInstance();
        IMap<String, String> customers = hazelcastInstance.getMap( "customers" );
        LocalMapStats mapStatistics = customers.getLocalMapStats();
        NearCacheStats nearCacheStatistics = mapStatistics.getNearCacheStats();
        System.out.println( "Near Cache hit/miss ratio = "
                + nearCacheStatistics.getRatio() );

The following are some of the metrics that you can access via the NearCacheStats object (applies to both client and member Near Caches):

  • creation time of the Near Cache on the member (getCreationTime())

  • number of entries owned by the member (getOwnedEntryCount())

  • memory cost (number of bytes) of owned entries in the Near Cache (getOwnedEntryMemoryCost())

  • number of hits (reads) of the locally owned entries (getHits())

See the NearCacheStats Javadoc to see all the metrics.

Multimap Statistics

To get MultiMap statistics, use the getLocalMultiMapStats() method from the MultiMap interface. This method returns a LocalMultiMapStats object that holds local MultiMap statistics.

Below is an example code where the getLocalMultiMapStats() method and the getLastUpdateTime method from LocalMultiMapStats get the last update time.

        HazelcastInstance hazelcastInstance = Hazelcast.newHazelcastInstance();
        MultiMap<String, String> customers = hazelcastInstance.getMultiMap( "customers" );
        LocalMultiMapStats multiMapStatistics = customers.getLocalMultiMapStats();
        System.out.println( "last update time =  "
                + multiMapStatistics.getLastUpdateTime() );

The following are some of the metrics that you can access via the LocalMultiMapStats object:

  • number of entries owned by the member (getOwnedEntryCount())

  • number of backup entries held by the member (getBackupEntryCount())

  • number of backups per entry (getBackupCount())

  • memory cost (number of bytes) of owned entries in the member (getOwnedEntryMemoryCost())

  • creation time of the multimap on the member (getCreationTime())

  • number of hits (reads) of the locally owned entries (getHits())

  • number of get and put operations on the map (getPutOperationCount() and getGetOperationCount())

See the LocalMultiMapStats Javadoc to see all the metrics.

Queue Statistics

To get local queue statistics, use the getLocalQueueStats() method from the IQueue interface. This method returns a LocalQueueStats object that holds local queue statistics.

Below is an example code where the getLocalQueueStats() method and the getAverageAge method from LocalQueueStats get the average age of items.

        HazelcastInstance node = Hazelcast.newHazelcastInstance();
        IQueue<Integer> orders = node.getQueue( "orders" );
        LocalQueueStats queueStatistics = orders.getLocalQueueStats();
        System.out.println( "average age of items = "
                + queueStatistics.getAverageAge() );

The following are some of the metrics that you can access via the `LocalQueueStats ` object:

  • number of owned items in the member (getOwnedItemCount())

  • number of backup items in the member (getBackupItemCount())

  • minimum and maximum ages of the items in the member (getMinAge() and getMaxAge())

  • number of offer, put and add operations (getOfferOperationCount())

See the LocalQueueStats Javadoc to see all the metrics.

Topic Statistics

To get local topic statistics, use the getLocalTopicStats() method from the ITopic interface. This method returns a LocalTopicStats object that holds local topic statistics.

Below is an example code where the getLocalTopicStats() method and the getPublishOperationCount method from LocalTopicStats get the number of publish operations.

        HazelcastInstance hazelcastInstance = Hazelcast.newHazelcastInstance();
        ITopic<Object> news = hazelcastInstance.getTopic( "news" );
        LocalTopicStats topicStatistics = news.getLocalTopicStats();
        System.out.println( "number of publish operations = "
                + topicStatistics.getPublishOperationCount() );

The following are the metrics that you can access via the `LocalTopicStats ` object:

  • creation time of the topic on the member (getCreationTime())

  • total number of published messages of the topic on the member (getPublishOperationCount())

  • total number of received messages of the topic on the member (getReceiveOperationCount())

See the LocalTopicStats Javadoc to see all the metrics.

Executor Statistics

To get local executor statistics, use the getLocalExecutorStats() method from the IExecutorService interface. This method returns a LocalExecutorStats object that holds local executor statistics.

Below is an example code where the getLocalExecutorStats() method and the getCompletedTaskCount method from LocalExecutorStats get the number of completed operations of the executor service.

        HazelcastInstance hazelcastInstance = Hazelcast.newHazelcastInstance();
        IExecutorService orderProcessor = hazelcastInstance.getExecutorService( "orderProcessor" );
        LocalExecutorStats executorStatistics = orderProcessor.getLocalExecutorStats();
        System.out.println( "completed task count = "
                + executorStatistics.getCompletedTaskCount() );

The following are some of the metrics that you can access via the `LocalExecutorStats ` object:

  • number of pending operations of the executor service (getPendingTaskCount())

  • number of started operations of the executor service (getStartedTaskCount())

  • number of completed operations of the executor service (getCompletedTaskCount())

See the LocalExecutorStats Javadoc to see all the metrics.