line
Review and adjust the default `DistributionStatisticConfig`
Currently, Armeria uses the default DistributionStatisticConfig of:
DistributionStatisticConfig
.builder()
.percentilesHistogram(false)
.sla()
.percentiles(new double[] { 0, 0.5, 0.75, 0.9, 0.95, 0.98, 0.99, 0.999, 1.0 })
.percentilePrecision(2)
.minimumExpectedValue(1L)
.maximumExpectedValue(Long.MAX_VALUE)
.expiry(Duration.ofMinutes(3))
.bufferLength(3)
.build();
When we define the above defaults, our intention was to rotate the buffer every minute, as explained in the comments:
/**
* Export the percentile values only by default. We specify all properties so that we get consistent values
* even if Micrometer changes its defaults. Most notably, we changed {@code percentilePrecision},
* {@code expiry} and {@code bufferLength} due to the following reasons:
* <ul>
* <li>The default {@code percentilePrecision} of 1 is way too inaccurate.</li>
* <li>Histogram buckets should be rotated every minute rather than every some-arbitrary-seconds
* because that fits better to human's mental model of time. Micrometer's 2 minutes / 3 buffers
* (i.e. rotate every 40 seconds) does not make much sense.</li>
* </ul>
*/
However, according to TimeWindowMax.rotate(): https://github.com/micrometer-metrics/micrometer/blob/v1.7.1/micrometer-core/src/main/java/io/micrometer/core/instrument/distribution/TimeWindowMax.java#L118-L145
it seems to me that the buffers are rotated every 3 minutes.
Action item: Double check if the buffers are rotated every minute with the current defaults. Change the defaults if we were mistaken.
@anuraaga @mauhiz Do you remember anything about this when we chose the above defaults?
By the way: I think the current trend is to define a MeterFilter to configure most of these properties, not to set them directly on DistributionConfig. https://micrometer.io/docs/concepts#_configuring_distribution_statistics
ref: https://github.com/line/armeria/pull/1226 (let me revisit here next monday)
