Hi I'm trying to understand the implementation of idleTimeMsPerSecond. Specifically what I'm trying to do is, adapt this metric to be used with Flink 1.9 (for a fork).
I tried an approach similar to this PR <https://github.com/apache/flink/pull/11564/files> and measuring the time to request a new buffer is easy to adapt but I've found that there's a difference in the way the mailbox loop runs in 1.9 vs. 1.12.1 and I end up with under-reported values (for example a sink getting no data, reports idleTimeMsPerSecond as 0 always which doesn't seem right). I see that the threading model in StreamTask has changed significantly after 1.9. Specifically, I think in Flink 1.9 there's no blocking Mailbox loop as in the later versions (example <https://github.com/apache/flink/blob/release-1.12.1/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/mailbox/MailboxProcessor.java#L310>) which is where the idle time is measured.. Maybe I'm missing something, but I guess I can't directly use the same approach to measure idle time in 1.9? If so, I guess an alternative (more expensive) approach may be to measure it when the task thread processes records (like somewhere in this block <https://github.com/apache/flink/blob/release-1.9.3/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/io/StreamOneInputProcessor.java#L133>) but I'm not sure if that would be the right/efficient thing to do.. Any suggestions on how to accurately measure task idle time in Flink 1.9? -- Lakshmi
