When working with Data Nodes (D-Nodes), you might experience unexpected technical issues that require detailed investigation. You can debug the issues if the log level for D-Nodes com.pega.dsm.dnode.impl.cassandra.Cassandra was set to DEBUG. For more information, see System Operations.

Cause

The most common problems and exceptions for D-Nodes are:

• Cassandra starts with corrupted SSTables; the log shows the following information statement:

  Failed to start Cassandra. Corrupted SSTables: <CorruptSSTableException>

• If the D-Node was added through the Services landing page, the following information statement is displayed for nodes with an exception at startup:

  Unable to enable as DNode

• The D-Node fails due to an exception; the log shows the following information statement:

  Cannot initialize DNode context and start Cassandra, PRPC continuing as non-DNode

• Data ownership is incorrect after adding a node. Data ownership is not evenly distributed across the number of nodes; the values do not add up to 100%.

• Snappy Compression support is unavailable in Pega^® Platform; the log shows the following information statement:

  java.lang.NoClassDefFoundError: org.xerial.snappy.Snappy (initialization failure)

Solution - Information statements 1 to 4

1. Click Designer Studio > Decisioning > Infrastructure > Services.
2. Decommission a node by clicking Decommission in the Action column.
3. Stop the node.
4. Remove the Cassandra data files. The location of the data files is defined by the data_files_directories parameter in the prconfig.xml file. For more information, see Configuration settings for Pega Platform nodes.
5. Restart the node.
6. Assign the node to the applicable service.

For more information, see Managing decision data nodes.

Solution - Snappy Compression support is unavailable in the platform

Install Snappy compression library or disable compression through the dnode/yaml/internode_compression setting in the prconfig.xml file. For more information, see Configuration settings for Pega Platform nodes.