The discussion has started here: https://github.com/apache/incubator-druid/pull/6677#discussion_r237182258 (TL;DR: there are a lot of references from java.lang.ref package, including finalizers, in the heaps of Druid nodes, that is bad for GC).
Now I'm 90% sure that the major source of finalizable objects is Curator: https://issues.apache.org/jira/browse/CURATOR-487 We are not exposed to that, but those who use Zstd compression with Druid could have a lot of finalizable objects coming from Zstd compression, see https://issues.apache.org/jira/browse/COMPRESS-473 and https://github.com/luben/zstd-jni/issues/83 Zstd compression / decompression could also be a subject of double-free race through finalize(): https://github.com/luben/zstd-jni/issues/82 I didn't check other compression/decompression/encryption/decryption parts used by Druid yet but there is a big chance that some of them are problematic too.
