srdo commented on PR #17139:
URL: https://github.com/apache/kafka/pull/17139#issuecomment-2590986916
You are completely correct. My mistake. TimeRatio can't "lose time" the way
I thought. The scenario I described was wrong, I misunderstood the code.
So if the two other concerns mentioned above (thread safety, the effect of
multiple metrics reporters) turn out to not be relevant, I guess TimeRatio is
fine as is?
Not sure if this matters in practice, but here's another example
demonstrating funny metric outputs:
```
@Test
public void testPartialPoll() {
MetricConfig config = new MetricConfig();
MockTime time = new MockTime();
TimeRatio ratio = new TimeRatio(1.0);
ratio.record(config, 0.0, time.milliseconds());
time.sleep(10);
// Pretend poll starts here
time.sleep(10);
//This emits the default value because the poll isn't done, so the
current window has size 0
assertEquals(1.0, ratio.measure(config, time.milliseconds()));
time.sleep(10);
ratio.record(config, 20, time.milliseconds());
// This is technically the correct value, but this measurement ends
up covering the entire time interval
// and we're still left with a meaningless 1.0 metric value above.
// When a user looks at this in their metrics, they'll see 1.0
followed by 0.66, which is pretty hard to interpret.
assertEquals(2 / 3.0, ratio.measure(config, time.milliseconds()));
// To demonstrate that this can be repeated
// Pretend another poll starts here
time.sleep(10);
// We again get a meaningless 1.0 metric since the window is 0 in
size
assertEquals(1.0, ratio.measure(config, time.milliseconds()));
time.sleep(10);
ratio.record(config, 10, time.milliseconds());
// followed by the "real" value in this call
assertEquals(0.5, ratio.measure(config, time.milliseconds()));
}
```
In this test, the user will observe the following emitted metric values:
1.0, 0.66, 1.0, 0.5, even though two of those values are meaningless. This
happens if `measure` is called twice in a row without a completed poll between
them.
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