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Hazelcast is an open-source distributed in-memory data store and computation platform. It provides a wide variety of distributed data structures and concurrency primitives, including:

  • a distributed, partitioned and queryable in-memory key-value store implementation, called IMap
  • additional data structures and simple messaging constructs such as Set, MultiMap, Queue, Topic
  • cluster-wide unique ID generator, called FlakeIdGenerator
  • a distributed, CRDT based counter, called PNCounter
  • a cardinality estimator based on HyperLogLog.

Additionally, Hazelcast includes a production-ready Raft implementation which allows implementation of linearizable constructs such as:

  • a distributed and reentrant lock implementation, called FencedLock
  • primitives for distributed computing such as AtomicLong, AtomicReference and CountDownLatch.

Hazelcast data structures are in-memory, highly optimized and offer very low latencies. For a single get or put operation on an IMap, you can typically expect a round-trip-time of under 100 microseconds.

It's very simple to form a cluster with Hazelcast, you can easily do it on your computer by just starting several instances. The instances will discover each other and form a cluster. There aren't any dependencies on any external systems.

Hazelcast automatically replicates data across the cluster and you are able to seamlessly tolerate failures and add additional capacity to the cluster when needed.

Hazelcast comes with clients in the following programming languages:

Hazelcast also has first-class support for running on different cloud providers such as AWS, GCP and Azure as well as on Kubernetes.


You can download Hazelcast from Once you have downloaded, you can start the Hazelcast instance using the script bin/

Get Started

Hazelcast allows you to interact with a cluster using a simple API, for example you can use the Hazelcast Java Client to connect to a running cluster and perform operations on it:

HazelcastInstance hz = HazelcastClient.newHazelcastClient();
IMap<String, String> map = hz.getMap("my-distributed-map");
map.put("key", "value");
String current = map.get("key");
map.putIfAbsent("somekey", "somevalue");
map.replace("key", "value", "newvalue");

You only need to add a single JAR as a dependency:


For more information, see the Getting Started Guide


See the reference manual for in-depth documentation about Hazelcast features.

Code Samples

See Hazelcast Code Samples

Hazelcast Jet

Hazelcast Jet is a distributed batch and stream processing framework based on Hazelcast. It can be used to import/export data from/to Hazelcast using a very wide variety of data sources including Hadoop, S3, Apache Kafka, Elasticsearch, JDBC and JMS.

Get Help

You can use the following channels for getting help with Hazelcast:


We encourage Pull Requests and process them promptly.

To contribute:

For an enhancement or larger feature, create a GitHub issue first to discuss.

Using Snapshot Releases

Maven snippet:

    <name>Sonatype Snapshot Repository</name>

Building From Source

Pull latest from repo git pull origin master and use Maven install (or package) to build mvn clean install.


Hazelcast has 3 testing profiles:

  • Default: Type mvn test to run quick/integration tests (those can be run in parallel without using network).
  • Slow Tests: Type mvn test -P slow-test to run tests that are either slow or cannot be run in parallel.
  • All Tests: Type mvn test -P all-tests to run all tests serially using network.

Checkstyle and SpotBugs

Hazelcast uses static code analysis tools to check if a Pull Request is ready for merge. Run the following commands locally to check if your contribution is Checkstyle and SpotBugs compatible.

mvn clean validate -P checkstyle
mvn clean compile -P spotbugs


Hazelcast is available under the Apache 2 License. Please see the Licensing section for more information.


Thanks to YourKit for supporting open source software by providing us a free license for their Java profiler


Copyright (c) 2008-2020, Hazelcast, Inc. All Rights Reserved.

Visit for more info.

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