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The Metrics Explorer of the CDAP UI can be used to examine and set metrics in a CDAP instance.

Flow Control

A flow control mechanism in CDAP prevents you from submitting too many requests, which can cause stuck or failed pipeline runs. This mechanism applies to start (Launch) requests for the following pipelines and jobs in all editions of CDAP, versions 6.6 and later:

• Batch pipelines

• Real-time pipelines

• Replication jobs

Thresholds

To control the number of outstanding start requests in CDAP, flow control relies on two thresholds:

• Launch threshold. Limits the number of launch requests being made. If the number of launch requests received by Cloud Data Fusion that are not yet in Running state is greater than the launch threshold (number of launch requests that aren't running yet > launch threshold), the request is rejected. The number includes batch pipelines, real-time pipelines, and Replication jobs.

• Runs threshold. Limits the number of outstanding launch requests in the system. If the number of outstanding launch requests received by Cloud Data Fusion that have not yet finished is greater than a specified runs threshold (number of outstanding requests that aren't finished yet > runs threshold), the request is rejected.

Rejected requests

If either threshold is met, every new start request gets rejected. For example, a rejected batch pipeline has a Rejected status in the logs, and a dialog in the UI describes why the launch was rejected.

Metrics

The number of launching and running pipelines along with the number of rejected pipelines in the system can be accessed through the metrics service as follows.

Launching metric

Reports the number of launching requests in the system. That is, it reports the number of launch requests that are in Provisioning or Starting states.

Metrics name: flowcontrol.launching.count

POST /v3/metrics/query?metric=system.flowcontrol.launching.count

Running metric

Reports the number of running pipelines and jobs in the system. The run threshold is based on the sum of the Launching and Running metrics values.

Metrics name: flowcontrol.running.count

POST /v3/metrics/query?metric=system.flowcontrol.running.count

Rejected metric

Reports the number of rejected runs due to the flow control mechanism.

Metrics name: program.rejected.runs

POST /v3/metrics/query?metric=system.program.rejected.runs