.. _node_actions:

Node administration
======================

In the Cluster area of OpsCenter, you select different views of
the nodes comprising your Cassandra cluster, and then, perform node management.

OpsCenter Enterprise Edition 3.0 can monitor and administer Cassandra 1.0 and later, but with Cassandra 1.2 it will not work as described in these procedures if you enable virtual nodes. When you enable virtual nodes, OpsCenter chooses a single token for each node for operations, such as collecting metrics. Attempting to move nodes, rebalance nodes, and perform other tasks involving token ranges is not supported.

Node management operations
----------------------------
Each of the cluster views--ring, physical, and list--has an Actions button. 

* In the Ring View or Physical View of a cluster, click the graphic representation of the node. The Actions button appears in the dialog.

* In the List View of a cluster, select a node. If necessary, expand the List View window to see the Actions button on the right side. 

Click the Actions button to access a drop-down list of node management operations. To avoid impacting cluster performance, perform actions that move data between nodes at low-usage times. Examples of such actions are move, decommission, and repair. 

This table describes actions on the drop-down list:


===================== =========================================================
Action 	              Description
===================== =========================================================
View Metrics          Redirects you to the Performance area of OpsCenter where
                      you can select metrics graphs and configure performance
                      views for the selected node.

View Replication      Shows the replication relationships between the selected
                      node and other nodes in the cluster. Visible in Ring
                      View and Physical View.

Configure             Allows you to change the configuration of the node.

Start                 Starts the DSE / Cassandra process on the node.

Stop                  Stops the DSE / Cassandra process on the node.

Restart               Restarts the DSE / Cassandra process on the node.

Cleanup               Removes rows that the node is no longer responsible for.
                      This is usually done after changing the partitioner 
                      tokens or the replication options for a cluster.

Compact               Performs a major compaction, which is *not* a 
                      recommended procedure in most Cassandra clusters.

Flush                 Causes the recent writes currently stored in memory
                      (memtables) to be flushed to disk as persistent SSTables.

Repair                Makes a node consistent with its replicas by doing an
                      in-memory comparison of all the rows of a column family, 
                      and resolving any discrepancies between replicas by
                      updating outdated rows with the current data.

Perform GC            Forces the Java Virtual Machine (JVM) on the selected
                      node to perform a garbage collection (GC). 
                      This reclaims physical disk space occupied by obsolete
                      SSTables, such as those that have been truncated or 
                      compacted (merged) into new SSTables.

Decommission          Removes a node from the cluster and streams its data to
                      neighboring replicas.

Drain                 Causes the recent writes currently stored in memory
                      (memtables) to be flushed to disk as persistent SSTables, 
                      and then makes the node read-only (the node will stop
                      accepting new writes).  This is usually done when
                      upgrading a node.

Move                  Changes the partitioner token assignment for the node,
                      thus changing the range of data that the node is 
                      responsible for.
===================== =========================================================



