Removed features

indices.fielddata.cache.expire

The experimental feature indices.fielddata.cache.expire has been removed. For indices that have this setting configured, this config will be ignored.

Forbid changing of thread pool types

Previously, thread pool types could be dynamically adjusted. The thread pool type effectively controls the backing queue for the thread pool and modifying this is an expert setting with minimal practical benefits and high risk of being misused. The ability to change the thread pool type for any thread pool has been removed; do note that it is still possible to adjust relevant thread pool parameters for each of the thread pools (e.g., depending on the thread pool type, keep_alive, queue_size, etc.).