使用Java驱动程序跟踪Cassandra查询时出现空指针错误

Question

I'm trying to measure the server side query execution time for a query in Cassandra using the java driver. I'm using rSet.getExecutionInfo().getQueryTrace().getDurationMicros() where rSet is the result set for the query I'm executing. I manually turned on tracing using cqlsh and was able to get the trace through cqlsh but I get a null value when I try it with the java driver. Is there something else I should be doing to enable tracing while using the java driver?

EDIT

Adding code used to query and connect to the cluster.

The code snippet I use to query and measure server side execution time

ResultSet rSet = session.execute("SELECT * from quelea.users where user_id = " + userId +" ALLOW Filtering");
System.out.println("Server-side query Execution time : " + rSet.getExecutionInfo().getQueryTrace()).getDurationMicros());

The code I use to connect to the Cassandra cluster

public void connect(final String node, final int port)  
   {  
      this.cluster = Cluster.builder().addContactPoint(node).withPort(port).build();  
      final Metadata metadata = cluster.getMetadata();  
      out.printf("Connected to cluster: %s\n", metadata.getClusterName());  
      for (final Host host : metadata.getAllHosts())  
      {  
         out.printf("Datacenter: %s; Host: %s; Rack: %s\n",  
            host.getDatacenter(), host.getAddress(), host.getRack());  
      }  
      session = cluster.connect();  
   }  

Answer 1

Based on your provided code:

ResultSet rSet = session.execute("SELECT * from quelea.users where user_id = " + userId +" ALLOW Filtering");

It appears that you are not enabling tracing, which is why getQueryTrace() returns null, thus why getDurationMicros() throws a NullPointerException . ( Note : when using TRACING on; in cqlsh, it only applies to your cqlsh session, not globally).

To enable tracing you can use enableTracing() , ie:

Statement statement = new SimpleStatement("SELECT * from quelea.users where user_id = " + userId +" ALLOW Filtering").enableTracing();
ResultSet rSet = session.execute(statement);