Q11. What does it mean that FlowFileRepository are Write-Ahead-Log?

Ans: It means anything written to the FlowFileRepository are first logged and check pointed. Persist in the logs to avoid any data loss, before processing the data as well as periodically check pointed to support rollback.

Q12. Does Reporting Task have access to the FlowFile contents?

Ans: No, a Reporting Task does not have access to individual FlowFile. Rather, a Reporting Task has access to all Provenance Events, bulletins, and the metrics shown for components on the graph, such as FlowFiles In, Bytes Read, and Bytes Written.

Q13. What is the use of FlowFileExpiration?

Ans: FlowFileExpiration attribute is defined on the Dataflow connection. And it helps us to decide that after x amount of time this FlowFile should be expired and deleted. Suppose you have configured FlowFileExpiration as 1 hr. As soon as FlowFile arrived in the NiFi system and timer will start. And as soon as FlowFile reaches to the connection. Connection will check how old is the FlowFile, if it is already 1 hr than that FlowFile will not be processed and will be deleted.

Q14. What is the Backpressure in NiFi system?

Ans: Sometime what happens that Producer system is faster than consumer system. Hence, the messages which are consumed is slower. Hence, all the messages (FlowFiles) which are not being processed will remain in the connection buffer. However, you can limit the connection backpressure size either based on number of FlowFiles or number of data size. If it reaches to defined limit, connection will give back pressure to producer processor not run. Hence, no more FlowFiles generated, until backpressure is reduced. This is one of the important feature of this.

Q15. If while processing FlowFile, prioritize finds that two FlowFile have the same priority. Which FlowFile will be processed first?

Ans: If there are multiple FlowFiles having the same priority based on the first prioritizes than the next one which is in the selected prioritizes will be considered to evaluate the priority (means another criteria will be used to find the priority).