Resurrecting this topic with some clarity on the issue and it's remedy.   If RegionServers would be keeping dead connections to the Datanodes, the same symnptoms would be seen, many connection in CLOSE_WAIT, and file descriptor number increasing. In extreme cases the limit could be reached, whioch would case the host node to fail with no more open file descriptors to use issue.   There wasa bug in HBase prior to CDH5.13 which is described in this upstream JIRA in more detail[1]: HBASE-9393 Hbase does not closing a closed socket resulting in many CLOSE_WAIT]   This issue was patched in the following CDH releases: CDH5.13.0, CDH5.13.1, CDH5.13.2, CDH5.13.3, CDH5.14.0,  CDH5.14.2, CDH5.14.4, CDH5.15.0,  CDH5.15.1, CDH6.0.0.   [1] - upstream HBase JIRA - https://issues.apache.org/jira/browse/HBASE-9393?attachmentOrder=asc ... View more