The Spark Cassandra Connector utilizes the Codahale metrics system to expose information on the latency and throughput of Cassandra operations.
Spark internal metrics are visible in Spark UI. The user is able to browse application stages and particular tasks along with the amount of data which was read, written and how long it took.
Because of a limitation in the Spark metrics system the amount of data that has been read or written in a task will be marked as a Hadoop operation. Spark doesn‘t allow custom labels in their metric system and the Connector is not actually passing data through Hadoop. However, it doesn’t really matter because it is just label.
The Connector metrics are also exposed through Spark's metric system in both the executor and the driver. To access these metrics add a new source called cassandra-connector in your metrics.properties file. Example:
executor.source.cassandra-connector.class=org.apache.spark.metrics.CassandraConnectorSource driver.source.cassandra-connector.class=org.apache.spark.metrics.CassandraConnectorSource
While there should be a minimal performance effect from collecting metrics, Metric collection can be disabled. Codahale metrics are not collected if CassandraConnectorSource is not specified in the metrics configuration file. In order to disable task metrics, use these properties in Spark configuration:
spark.cassandra.input.metrics - set to false to disable collection of input task metricsspark.cassandra.output.metrics - set to false to disable collection of output task metrics| Metric name | Unit description |
|---|---|
| write-byte-meter | Number of bytes written to Cassandra |
| write-row-meter | Number of rows written to Cassandra |
| write-batch-timer | Batch write time length |
| write-batch-wait-timer | The length of time batches sit in the queue before being submitted to Cassandra |
| write-batch-size-histogram | The distribution of the rows in batches |
| write-task-timer | Timer to measure time of writing a single partition |
| write-success-counter | Number successfully written batches |
| write-failure-counter | Number of failed batches |
| read-byte-meter | Number of bytes read from Cassandra |
| read-row-meter | Number of rows read from Cassandra |
| read-task-timer | Timer to measure time of reading a single partition |