Node stuck in LEAVING state after being decommissioned

Problem

Summary

Several hours after decommissioning a node, the node still shows as UL or LEAVING state despite having very little data.

Symptoms

In the context of this article, a stuck or hung decommission is characterised by:

• DataStax Enterprise (DSE) or Apache Cassandra process is still running
• no activity in the system.log
• nodetool status shows the node in UL or LEAVING state
• nodetool netstats shows the node in LEAVING mode and not sending streams
• nodetool compactionstats shows 0 pending tasks
• very low or close to zero CPU utilisation

Cause

A common cause of this problem is administrators incorrectly running nodetool drain prior to decommissioning a node.

When a node is "drained", data is flushed to disk and Apache Cassandra stops listening for connections from clients and other nodes in the cluster. Despite the Apache Cassandra process and JVM still running, for all intents and purposes Apache Cassandra is no longer operational.

The nodetool drain command is used to prepare a node for a Apache Cassandra or DSE upgrade. Do not run the command as part of a decommission process.

Workaround

Use these steps to get the node to decommission.

Step 1 - Restart Apache Cassandra/DSE on the node.

Step 2 - Run nodetool decommission again and the node should be removed from the cluster as expected.

See also

DataStax doc - nodetool drain command