Breaking changes in 5.5

Ignoring hidden folders

Previous versions of Elasticsearch would skip hidden files and directories when scanning the plugins folder. This allows broken plugin installs to remain undetected so this leniency has been removed.

Skip setting kernel parameters

Elasticsearch attempts to set the kernel parameter vm.max_map_count during installation. In some environments this can fail. Previous versions of Elasticsearch accepted a flag ES_SKIP_SET_KERNEL_PARAMTERS to skip this writing. Starting in Elasticsearch 5.5.0, this flag has been removed and instead the same functionality can be achieved by masking the systemd-sysctl service.

Java API changes

The has_child, has_parent and parent_id queries have moved to parent-join module. Also the children aggregation has been moved to the parent-join module. The parent-join module should be loaded when using the transport client. Alternatively use the PreBuiltTransportClient client, which load the module automatically.