[OTel] Only set resource info on root spans

[PROFeNoM]

Description

This PR removes redundant resource info from being set on all OTel (native or remapped) spans. It fundamentally is a breaking change (since we are removing data from some spans), so if we want to do it, now is the time.

What is Resource Info?
From OTel Doc:

• environment
• host information
• host operating system
• current process
• runtime

Why should we remove it?

• First, a customer would ingest "many" irrelevant bytes.

Here is a sample payload without resources (9 tags)

{
                "trace_id": "65ddafdb0000000007b244ca5366620e",
                "span_id": "805384663926885947",
                "parent_id": "9429929380169505464",
                "start": 1709027293.039369,
                "end": 1709027293.039381,
                "duration": 1.2125e-05,
                "type": "web",
                "service": "customer_app_web_service",
                "name": "laravel.event.handle",
                "resource": "Illuminate\\Foundation\\Http\\Events\\RequestHandled",
                "resource_hash": "5da477cef10a0ff3",
                "host_id": 439449322,
                "hostname": "docker-desktop",
                "env": "prod",
                "host_groups": [
                    "env:prod"
                ],
                "meta": {
                    "ddtags": "ingestion_reason:auto",
                    "component": "laravel",
                    "env": "prod",
                    "language": "php",
                    "_dd.p.ftid": "65ddafdb0000000007b244ca5366620e",
                    "_dd.agent_version": "7.50.3",
                    "_dd.agent_hostname": "docker-desktop",
                    "_dd.tracer_version": "0.98.0"
                },
                "metrics": {
                    "_sampling_priority_v1": 1.0
                },
                "ingestion_reason": "auto",
                "metadata": {
                    "sds_info": []
                },
                "children_ids": []
            }

Same operation with resource info (25 tags)

{
                "trace_id": "65ddafdb0000000007b244ca5366620e",
                "span_id": "12568249948290625744",
                "parent_id": "15313292926888664709",
                "start": 1709027292.995515,
                "end": 1709027292.996892,
                "duration": 0.001376375,
                "type": "web",
                "service": "customer_app_web_service",
                "name": "laravel.event.handle",
                "resource": "Illuminate\\Database\\Events\\QueryExecuted",
                "resource_hash": "c49a35ffdaafe898",
                "host_id": 439449322,
                "hostname": "docker-desktop",
                "env": "prod",
                "host_groups": [
                    "env:prod"
                ],
                "meta": {
                    "process.executable.path": "/usr/local/sbin/php-fpm",
                    "component": "laravel",
                    "_dd.tracer_version": "0.98.0",
                    "host.arch": "aarch64",
                    "_dd.agent_version": "7.50.3",
                    "process.runtime.name": "fpm-fcgi",
                    "os.name": "Linux",
                    "telemetry.distro.version": "1.0.0",
                    "process.owner": "www-data",
                    "os.type": "linux",
                    "telemetry.sdk.language": "php",
                    "os.description": "6.5.11-linuxkit",
                    "telemetry.sdk.name": "opentelemetry",
                    "telemetry.sdk.version": "1.0.8",
                    "language": "php",
                    "ddtags": "ingestion_reason:auto",
                    "process.runtime.version": "8.2.12",
                    "_dd.p.ftid": "65ddafdb0000000007b244ca5366620e",
                    "env": "prod",
                    "os.version": "#1 SMP PREEMPT Wed Dec  6 17:08:31 UTC 2023",
                    "telemetry.distro.name": "opentelemetry-php-instrumentation",
                    "service.version": "1.0.0+no-version-set",
                    "host.name": "61cd348cc3c2",
                    "_dd.agent_hostname": "docker-desktop"
                },
                "metrics": {
                    "_sampling_priority_v1": 1.0,
                    "process.pid": 9859.0
                },
                "ingestion_reason": "auto",
                "metadata": {
                    "sds_info": []
                },
                "children_ids": [
                    "12622166295660867307",
                    "12074790514185832795",
                    "4622667366984769435",
                    "10340755233058322318"
                ]
            }

That's a 178% increase! 🚀

• Second, this information was already there in the root span. We have no value from having it in the children

• Some of this same information is already available from other tabs (e.g., Infrastructure or Processes).

• Finally, it has a performance impact (as shown by the benchmarks) because of the instances and added serialization work needed.

Reviewer checklist

• Test coverage seems ok.
• Appropriate labels assigned.

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-03-06 12:10:12

Comparing candidate commit bccb004 in PR branch alex/otel/resource-on-root-span with baseline commit 61382d5 in branch ddtrace-1.0.0.

Found 11 performance improvements and 1 performance regressions! Performance is the same for 166 metrics, 0 unstable metrics.

scenario:PDOBench/benchPDOBaseline

• 🟩 execution_time [-16.151µs; -15.085µs] or [-8.472%; -7.913%]

scenario:PDOBench/benchPDOOverhead

• 🟩 execution_time [-16.685µs; -14.975µs] or [-5.793%; -5.199%]

scenario:PDOBench/benchPDOOverheadWithDBM

• 🟩 execution_time [-16.944µs; -14.880µs] or [-5.456%; -4.792%]

scenario:PDOBench/benchPDOOverheadWithDBM-opcache

• 🟥 execution_time [+15.684µs; +17.495µs] or [+5.014%; +5.593%]

scenario:SpanBench/benchOpenTelemetryAPI

• 🟩 execution_time [-27.757µs; -23.294µs] or [-8.474%; -7.112%]
• 🟩 mem_peak [-4.806MB; -4.806MB] or [-12.497%; -12.497%]

scenario:SpanBench/benchOpenTelemetryAPI-opcache

• 🟩 execution_time [-16.504µs; -10.899µs] or [-6.036%; -3.986%]
• 🟩 mem_peak [-4.807MB; -4.807MB] or [-13.869%; -13.869%]

scenario:SpanBench/benchOpenTelemetryInteroperability

• 🟩 execution_time [-673.058µs; -664.682µs] or [-77.777%; -76.809%]
• 🟩 mem_peak [-18.386MB; -18.386MB] or [-37.697%; -37.697%]

scenario:SpanBench/benchOpenTelemetryInteroperability-opcache

• 🟩 execution_time [-541.240µs; -533.740µs] or [-74.084%; -73.058%]
• 🟩 mem_peak [-16.313MB; -16.313MB] or [-37.981%; -37.981%]

[bwoebi]

Let's do that :-)