Nulls and unset

Null and unset values

To complete a distributed delete operation, Cassandra replaces it with a special value called a tombstone which can be propagated to replicas. When inserting or updating a field, Cassandra allows you to set a certain field to null as a way to clear the value of a field and it is considered a delete operation.

In some cases, you might be inserting rows using null for values that are not specified, and even though our intention is to leave the value empty, Cassandra represents it as a tombstone causing an unnecessary overhead. To avoid tombstones, in previous versions of Cassandra, you can use different query combinations only containing the fields that have a value.

Unset

Cassandra 2.2 introduced the concept of “unset” for a parameter value. At server level, this field value is not considered. This can be represented in the C# driver with the class Unset.

// Prepare once in your application lifetime
var ps = session.Prepare("INSERT INTO tbl1 (id, val1) VALUES (?, ?)");

// Bind the unset value in a prepared statement
session.Execute(ps.Bind(id, Unset.Value));