APM: don't delete decision maker tag from span

[ajgajg1134]

What does this PR do?

Don't remove _dd.p.dm from the span tags it's found on. This was originally added when simplifying the logic here for later parts of the agent (where it seemed this was allowed, but given that functionally we didn't do this before this ended up being a breaking change :( )

Motivation

There are some upstream systems that do not look at the trace chunk level attributes so by deleting the span level tag here we inadvertently break those systems.

Additional Notes

Possible Drawbacks / Trade-offs

There's a marginal increase in the amount of data here

Describe how to test/QA your changes

Verify that the upstream systems for this are able to detect the decision maker (check with me for confirmation)

[pr-commenter]

Test changes on VM

Use this command from test-infra-definitions to manually test this PR changes on a VM:

inv create-vm --pipeline-id=34057565 --os-family=ubuntu

[pr-commenter]

Regression Detector

Regression Detector Results

Run ID: 7b567828-ea6e-4f1f-a39b-9d46f3baa5d9
Baseline: 49f6e7f
Comparison: 9bcecea

Performance changes are noted in the perf column of each table:

• ✅ = significantly better comparison variant performance
• ❌ = significantly worse comparison variant performance
• ➖ = no significant change in performance

Significant changes in experiment optimization goals

Confidence level: 90.00%
Effect size tolerance: |Δ mean %| ≥ 5.00%

perf	experiment	goal	Δ mean %	Δ mean % CI
❌	tcp_syslog_to_blackhole	ingress throughput	-98.30	[-102.45, -94.15]

Experiments ignored for regressions

Regressions in experiments with settings containing erratic: true are ignored.

perf	experiment	goal	Δ mean %	Δ mean % CI
➖	file_to_blackhole	% cpu utilization	-2.05	[-7.44, +3.33]

Fine details of change detection per experiment

perf	experiment	goal	Δ mean %	Δ mean % CI
➖	uds_dogstatsd_to_api_cpu	% cpu utilization	+1.36	[-1.53, +4.25]
➖	basic_py_check	% cpu utilization	+0.86	[-1.78, +3.50]
➖	pycheck_1000_100byte_tags	% cpu utilization	+0.49	[-4.12, +5.11]
➖	file_tree	memory utilization	+0.44	[+0.34, +0.54]
➖	uds_dogstatsd_to_api	ingress throughput	+0.01	[-0.20, +0.21]
➖	trace_agent_msgpack	ingress throughput	-0.00	[-0.00, +0.00]
➖	trace_agent_json	ingress throughput	-0.00	[-0.01, +0.01]
➖	tcp_dd_logs_filter_exclude	ingress throughput	-0.04	[-0.08, -0.00]
➖	otel_to_otel_logs	ingress throughput	-0.13	[-0.49, +0.23]
➖	idle	memory utilization	-0.15	[-0.19, -0.11]
➖	file_to_blackhole	% cpu utilization	-2.05	[-7.44, +3.33]
❌	tcp_syslog_to_blackhole	ingress throughput	-98.30	[-102.45, -94.15]

Explanation

A regression test is an A/B test of target performance in a repeatable rig, where "performance" is measured as "comparison variant minus baseline variant" for an optimization goal (e.g., ingress throughput). Due to intrinsic variability in measuring that goal, we can only estimate its mean value for each experiment; we report uncertainty in that value as a 90.00% confidence interval denoted "Δ mean % CI".

For each experiment, we decide whether a change in performance is a "regression" -- a change worth investigating further -- if all of the following criteria are true:

1. Its estimated |Δ mean %| ≥ 5.00%, indicating the change is big enough to merit a closer look.

2. Its 90.00% confidence interval "Δ mean % CI" does not contain zero, indicating that if our statistical model is accurate, there is at least a 90.00% chance there is a difference in performance between baseline and comparison variants.

3. Its configuration does not mark it "erratic".

[knusbaum]

/merge

[dd-devflow]

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