5.1 Release Notes

New Features

  • Tiered Storage (BETA): Introduced the Tiered Storage feature which is an extension to Hazelcast Map assigning data to various types of storage media based on access patterns. It is a Hazelcast Enterprise feature and in BETA state. See Tiered Storage.

  • Persistence for Dynamic Configuration: You can now reload the updates made in configuration dynamically (at runtime) after a cluster restart. See Configuring Dynamic Configuration.


SQL Engine


  • Hazelcast command line interface is now available within the Hazelcast distribution package; previously it needed to be installed separately. #20062

Cloud Discovery Plugins

  • Added EndpointSlices support for the Kubernetes discovery plugin; now the EndpointSlices API usage is default, and the old Endpoints API is not used as a fallback if EndpointSlices are not available. #19643


  • Added zero-configuration support for the Java records in compact serialization. #20724

  • Updated the names of methods and fields in the Compact Serialization API to make them non-Java centric. #20257

  • Added the declarative configuration elements for Compact Serialization. #20016

  • Introduced the FieldKind class to get the field types for portable and compact serializations; previously it was FieldType. #19517

Data Structures

  • Added the support of include-value parameter for MultiMap item listeners; you can set it to true if you want the item event to contain the item values. #18815


  • Added support of the jar scheme in the JCache URI configuration. Without this support, when, for example, hazelcast-client.zip is provided in Spring boot application properties file and packaged as a boot JAR, then the Hazelcast caching provider was failing to load the file. #20543

  • Introduced a system property for allowing you to audit that all the Hazelcast instances running in your environment have the instance tracking file name set correctly in the configuration. See the note in Instance Tracking. #19928

  • Introduced the module integrity checker configuration property. Integrity checker is a component which verifies that the executable contains all the required META-INF/services. #19971


  • Added support of customizing the logging pattern and specifying configuration files via environment variables. We also added support for JsonTemplateLayout for which the JSON template can be customized. #20528

Management Center

  • Added the data-access-enabled property for the Management Center configuration on the member side. This allows you to enable or disable the access of Management Center to the data stored by the data structures in the cluster. Management Center can’t access the data if at least one member has the data access disabled. Its default value is true (enabled). #19991

  • Added the console-enabled property for the Management Center configuration on the member side. This allows you to disable the console feature on Management Center as it supports lots of operations and it’s not subject to the regular access restrictions; it can read from/write to any data structure even if Management Center is restricted to access those via client permissions. #19718


  • Hazelcast now shows the possible solutions in the terminal, if the license key is not set while starting a Hazelcast Enterprise cluster. #4614

  • Added the ability to persist the renewal of a Hazelcast license key when this change is made without shutting down the cluster. Renewing a license key has already been possible using the REST API. This enhancement makes such license renewals to be persisted so that when a member or the cluster is restarted, you will not need to re-update the license. #20446

Other Enhancements

  • Added safe-serialization property to protect MulticastDiscoveryStrategy against Java deserialization attacks. #20728

  • Upgraded the Elasticsearch client in Hazelcast’s elasticsearch-7 Jet engine connector. Since the client license was changed from Apache 2.0 to Elastic 2.0 in Elasticsearch 7.11, we also added the new license to explain the changes. #20427

  • Updated log4j2 dependency version to 2.17.1 in Hazelcast’s root pom.xml. #20184

  • With the introduction of Tiered Storage feature, we’ve improved the partition migration system to support chunked partition migrations. By this way, the data is sent as a stream of chunks while the partitions are migrated upon member failures or new member additions. Previously, at most 250 MB was recommended as the maximum size for a partition; however, if a partition is backed by Tiered Storage, this size may go beyond this limit and may cause out of memory errors during the migrations of partitions having large data. Chunked partition migrations eliminate these errors. #20005

  • The hz-start script now accepts absolute paths when providing the Hazelcast configuration file’s location. #19908

  • JSON strings can now work with paging predicate queries. #19880

  • You can now check if Hazelcast is started properly in the Docker environment simply by using a curl command, e.g., curl -f http://hazelcast-host:5701/hazelcast/health/ready. #19664

  • Hazelcast’s memcached implementation was interpreting the number values and parameters for incr and decr wrongly (numbers were being converted into byte arrays instead of decimals). This has been fixed by making these commands' implementations strictly follow the memcached protocol specification. #19653

  • Since the name of Hot Restart Persistence feature changed to Persistence, the prefix for its metrics also has been changed from "hot-restart" to "persistence". #19543

  • Aligned the Near Cache and query cache behaviors when the in-memory format is OBJECT:

    • Improved query cache methods to eliminate extra deserialization

    • Added serializeKeys flag to query cache configuration to align the behavior with Near Cache. #20265

  • Improved the speed of connection by a member when it joins the cluster, by removing the unnecessary sleep statements in the code. #18932


  • Fixed the NullPointerException issue when running the SELECT statement if there is a mapping for a map with partitioned indexes. #20601

  • Fixed an issue where a single SQL query having a mix of JSON string and HazelcastJsonValue for the INSERT statement was not working. #20303

  • Fixed various issues when using hostnames in Hazelcast’s network and WAN Replication configurations. With this fix, you can seamlessly use hostnames wherever the IP addresses of the members are used. #20014, #15722

  • Fixed an issue where the hazelcast.yaml file was ignored when it is the only configuration file present in the Hazelcast setup; during startup it was looking only for the hazelcast.xml file and producing an error message saying that the configuration does not exist even though there is the yaml configuration file. Now it automatically uses hazelcast.yaml when hazelcast.xml is not available. #20003

  • Fixed an issue where the Hazelcast command line interfaces commands were outputting incorrect command names when you want to see their usages using the --help argument. For example, the command hz-start --help was outputting the following:

    Usage: hazelcast-start [-d]
      -d, --daemon   Starts Hazelcast in daemon mode

    instead of the following:

    Usage: hz-start [-d]
      -d, --daemon   Starts Hazelcast in daemon mode
  • Fixed an issue where querying a map with SELECT (SQL) was failing when the data has compact serialization and the cluster has more than one member (with the class not being on the classpath). #19952

  • In Kubernetes environment, when the health check endpoint was taking too long to respond, the Hazelcast members were considered to be unresponsive and terminated; this issue has been fixed. #19829

  • Fixed an issue where the command hz-stop --help was not displaying the help but executing the hz-stop command. #19749

  • When you both enable the persistence and automatic removal of stale data in the configuration, member startup failures were occurring. This has been fixed by adding the auto-remove-stale-data element to the configuration schema. #19683

  • Fixed an issue where the totalPublishes statistics for the Reliable Topic data structure were always generated as 0. #19642

  • Fixed an issue where some Spring XML configuration elements having values as property placeholders were not working when Hazelcast is upgraded to a newer version. #19629

  • Fixed an issue where the totalPublishes statistics for the Reliable Topic data structure were always generated as 0. #19555

  • Fixed an issue where the serialization was failing when the object has enum fields, or it is an enum itself. #19314

Removed/Deprecated Features

  • Removed the elasticsearch-5 module from Hazelcast distributions since the version 5.0 Elasticsearch has passed its end of life date; see its release notes. #20458

  • Deprecated the log(LogEvent logEvent) method in the ILogger class (com.hazelcast.logging.ILogger).


We would like to thank the contributors from our open source community who worked on this release: