### Migrating to OpenSearch and limits on the number of nested JSON objects
Migrating from Elasticsearch OSS version 6.8 to OpenSearch version 1.x will fail when a cluster contains any document that includes more than 10,000 nested JSON objects across all fields. Elasticsearch version 7.0 introduced the `index.mapping.nested_objects.limit` setting to guard against out-of-memory errors and assigned the setting a default of `10000`. OpenSearch adopted this setting at its inception and enforces the limitation on nested JSON objects. However, because the setting is not present in Elasticsearch 6.8 and not recognized by this version, migration to OpenSearch 1.x can result in incompatibility issues that block shard relocation between Elasticsearch 6.8 and OpenSearch versions 1.x when the number of nested JSON objects in any document surpasses the default limit.
Therefore, we recommend evaluating your data for these limits before attempting to migrate from Elasticsearch 6.8.
The `type` parameter has been removed from all OpenSearch API endpoints. Instead, indexes can be categorized by document type. For more details, see issue [#1940](https://github.com/opensearch-project/opensearch/issues/1940).
In OpenSearch 2.0, the Alerting plugin is now integrated with new plugins for Notifications. If you want to continue to use the notification action in the Alerting plugin, install the new backend plugins `notifications-core` and `notifications`. If you want to manage notifications in OpenSearch Dashboards, use the new `notificationsDashboards` plugin. For more information, see [Notifications]({{site.url}}{{site.baseurl}}/observing-your-data/notifications/index/) on the OpenSearch documentation page.
A Lucene upgrade forced OpenSearch to drop support for JDK 8. As a consequence, the [Java high-level REST client]({{site.url}}{{site.baseurl}}/clients/java-rest-high-level/) no longer supports JDK 8. Restoring JDK 8 support is currently an `opensearch-java` proposal [#156](https://github.com/opensearch-project/opensearch-java/issues/156) and will require removing OpenSearch core as a dependency from the Java client (issue [#262](https://github.com/opensearch-project/opensearch-java/issues/262)).
OpenSearch 2.5 contains a bug fix to correct the behavior of the `case_insensitive` parameter for the `wildcard` query on text fields. As a result, a wildcard query on text fields that ignored case sensitivity and erroneously returned results prior to the bug fix will not return the same results. For more information, see issue [#8711](https://github.com/opensearch-project/OpenSearch/issues/8711).
