There is a memory-leak in Jetty 9 that manifests whenever you hit the call queue limit in HBase REST. The memory-leak leaks both on-heap and off-heap objects permanently. It happens because whenever the call queue for Jetty server overflows, the task that is rejected runs a 'reject' method if it is a Rejectable to do any cleanup. This clean up is necessary to for example close the connection, deallocate any buffers, etc. Unfortunately, in Jetty 9, they implemented the 'reject' / cleanup method of the SelectChannelEndpoint as a non-blocking call that is not guaranteed to run. This was later fixed in Jetty 9.4 and later backported however the version of Jetty 9 pulled in HBase for REST comes before this fix. See https://github.com/eclipse/jetty.project/issues/1804 and https://github.com/apache/hbase/blob/master/pom.xml#L1416.
If we want to stay on 9.3.X we could update to 9.3.22.v20171030 which is the latest version of 9.3. Thoughts?