[APM] Trace timeline: Collapse spans faster than 95% of total trace duration

[formgeist]

APM UI – Distributed tracing – Timeline visualization meta issue #20553

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Summary

In an effort to condense the Timeline visualization, we'd want to collapse spans that are fast, since we deem them not important to analyze performance bottlenecks. The information still needs to be available, but we'll condense the spans that are faster than 95% of the total trace duration.

We'll only collapse if consecutive spans are eligible to be collapsed. So if a single span is eligble, we'll let it be. In most cases you might have a repeating pattern of fast resources that might as well be condensed.

Design

Displaying collapsed spans happens in the nested relation visualization on the left of the timeline.

Use the grab icon from EuiIcon to indicate collapsed spans. Show number of collapsed spans. Let the span graphs show on the Timeline.

The icon and summary will be a toggle to expand those spans anyway, but only that set of collapsed spans. There's no control to collapse the spans again, besides reloading the page. We might consider adding controls for both the % of duration the spans are collapsed along with an option to expand / collapse all at a later stage depending feedback.

[elasticmachine]

Pinging @elastic/apm-ui

[alvarolobato]

I've lowered the priory of this specific one within DT.

[sorenlouv]

Deferred to 6.6

[formgeist]

We fixed most of the issues with long trace waterfalls by implementing #106862 so no need to continue with the threshold approach at this time.