Testing performance impact using tracing

Tracing records all activity related to a request. These steps use tracing to show queries on a keyspace with a replication factor of 3 using different consistency levels (CL):

  • ONE processes responses from one of three replicas

  • QUORUM from two of three replicas

  • ALL from three of three replicas

    1. On the cqlsh command line, create a keyspace that specifies using three replicas for data distribution in the cluster.

        'class': 'SimpleStrategy', 
        'replication_factor': 3
    2. Create a table and insert a row.

      USE cycling_alt;
      CREATE TABLE IF NOT EXISTS cycling_alt.cyclist_name (
        id int PRIMARY KEY,
        lastname text,
        firstname text
    3. Turn on tracing and use the CONSISTENCY command to ensure the consistency level is ONE, the default.


      The output is:

      Current consistency level is ONE.
    4. Query the table to read the row.

      SELECT * FROM cycling_alt.cyclist_name WHERE id = 1;
 id | firstname | lastname
  1 |   Melissa |  HOSKINS

(1 rows)

+ The tracing results list all the actions taken to complete the SELECT statement.

  1. Change the consistency level to QUORUM to trace what happens during a read with a QUORUM consistency level.

    SELECT * FROM cycling_alt.cyclist_name WHERE id = 1;
Consistency level set to QUORUM.
  1. Change the consistency level to ALL and run the SELECT statement again.

    SELECT * FROM cycling_alt.cyclist_name WHERE id = 1;
Consistency level set to ALL.

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