Elasticsearch version 7.17.15

High Memory Pressure due to a GC change in JDK 21

This version of Elasticsearch is bundled with JDK 21. In JDK 21 Preventive GC has been removed. This may lead to increased memory pressure and an increased number of CircuitBreakerExceptions when retrieving large documents under some particular load. (issue: #99592)

If you needed to explicitly enable Preventive GC for your workload in a previous Elasticsearch version, we recommend you avoid to upgrade to this version, as the settings to enable Preventive GC have been removed from JDK 21.
The deprecated index.mapper.dynamic setting can break your cluster. It can only be set using the Update index settings API. Symptoms include nodes failing to start or shards failing to allocate. Do not use this setting in versions prior to 7.17.22. The bug is fixed in 7.17.22. (issue: #109160)

ILM+SLM

WaitForSnapshotStep now verifies that the index belongs to the latest snapshot of that SLM policy #100911 (issue: #57809)

Network

Ensure that all failures in TcpTransport#openConnection are treated consistently (all exceptions are now passed to the listener). #101907 (issue: #100510)
Protect NodeConnectionsService from stale connections #92558 (issue: #92029)

Snapshot/Restore

Packaging