Jason Gustafson created KAFKA-14664:
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Summary: Raft idle ratio is inaccurate
Key: KAFKA-14664
URL: https://issues.apache.org/jira/browse/KAFKA-14664
Project: Kafka
Issue Type: Bug
Reporter: Jason Gustafson
Assignee: Jason Gustafson
The `poll-idle-ratio-avg` metric is intended to track how idle the raft IO
thread is. When completely idle, it should measure 1. When saturated, it should
measure 0. The problem with the current measurements is that they are treated
equally with respect to time. For example, say we poll twice with the following
durations:
Poll 1: 2s
Poll 2: 0s
Assume that the busy time is negligible, so 2s passes overall.
In the first measurement, 2s is spent waiting, so we compute and record a ratio
of 1.0. In the second measurement, no time passes, and we record 0.0. The idle
ratio is then computed as the average of these two values (1.0 + 0.0 / 2 =
0.5), which suggests that the process was busy for 1s.
Instead, we should sum up the time waiting over the full interval. 2s passes
total here and 2s is idle, so we should compute 1.0.
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