[jira] [Resolved] (KAFKA-14664) Raft idle ratio is inaccurate

["Jason Gustafson (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KAFKA-14664?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jason Gustafson resolved KAFKA-14664.
-------------------------------------
    Resolution: Fixed

> 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
>            Priority: Major
>             Fix For: 3.5.0
>
>
> 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, which overestimates the true busy time.
> 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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