Cassandra Requests Test

All nodes in Cassandra are peers. A client read or write request can go to any node in the cluster. When a client connects to a node and issues a read or write request, that node serves as the coordinator for that particular client operation. The job of the coordinator is to act as a proxy between the client application and the nodes (or replicas) that own the data being requested. The coordinator determines which nodes in the ring should get the request based on the cluster configured partitioner and replica placement strategy.

In environments where multiple nodes are deployed, the nodes may receive thousands of read and write requests at a single time. To cater to the requests, it is always important for the nodes to be active. If multiple nodes are not available, then the requests may take too long to be serviced or at the worst case, the requests may fail. Therefore, it becomes important to keep track on the time taken by the nodes to service the requests and the count of requests that failed or timed out. The Cassandra Requests test helps administrators in this regard!

For each type of requests received by the target Cassandra Database server, this test reports the time taken to service the requests, the count of the requests that were unavailable, timed out and failed. By closely monitoring the measures reported by this test, administrators can further investigate the reason on why the requests were failed/timed out and take remedial measures to ensure that the requests are serviced at a faster pace!

Target of the test : A Cassandra Database

Agent deploying the test : An external/remote agent.

Outputs of the test : One set of results for each Request type on the target Cassandra Database node being monitored.

Configurable parameters for the test

Parameters	Description
Test Period	How often should the test be executed.
Host	The host for which the test is to be configured.
Port	The port on which the specified host listens. By default, this is 9042.
JMX Remote Port	Here, specify the port at which the JMX listens for requests from remote hosts. Ensure that you specify the same port that you configured in the cassandra-env.sh file (if the target Cassandra Database node is installed on a Unix host) or the cassandra-env.ps1 file (if the target Cassandra Database node is installed on a Windows host) in the <CASSANDRA_HOME> directory used by the target Cassandra Database node. To know how to specify the remote port, refer to Enabling JMX Support for JRE.
JMX User and JMX Password	If JMX requires authentication only (but no security), then ensure that the user and password parameters are configured with the credentials of a user with read-write access to JMX. To know how to create this user, refer to Configuring the eG Agent to Support JMX Authentication.
Confirm Password	Confirm the Password by retyping it in this text box.

Measurements made by the test

Measurement	Description	Measurement Unit	Interpretation
Total latency	Indicates the total time taken for servicing the requests of this type during the last measurement period.	Milliseconds	A low value is desired for this measure. If the value of this measure increases all of a sudden or gradually, then, it indicates that some peer nodes of the target Casandra database server are not servicing the requests or most of the requests are failing due to unavailability of the requested data etc.
Unavailable requests	Indicates the rate at which requests of this type were unavailable during the last measurement period.	Requests/sec	An unavailable request is the only request that will cause a write to fail, so any occurrences are serious. Cassandra’s inability to meet consistency requirements can mean that several nodes are down or otherwise unreachable, or that stringent consistency settings are limiting the availability of the node.
Timed-out requests	Indicates the rate at which requests of this type were timed out during the last measurement period.	Timeouts/sec	A low value is desired for this measure.
Failed requests	Indicates the rate at which requests of this type failed during the last measurement period.	Failures/sec	Ideally, the value of this measure should be zero.