Span metrics calls count always 0 with delta aggregation temporality

[jsonlsy]

Component(s)

connector/spanmetrics

What happened?

Description

Kudos to @san-san for finding this bug.

Looks like this PR introduced a bug when using delta aggregation temporality: #39052

With delta aggregation temporality, resourceMetrics get purged after exporting the metrics here. So, the metrics generated are always newly created ones and have isFirst set to true. This results in the value always getting overwritten here.

Can confirm that this is not an issue in v0.123.0 (i.e. prior to the first value logic)

Steps to Reproduce

• Run collector with the span metrics connector
• Send a span to the collector
• Wait for span metrics to be flushed. The value of the calls metrics is 0 instead of 1.
• Send another span with the same relevant attributes
• Wait for span metrics to be flushed. The value of the new calls metrics is 0 instead of 1.

Expected Result

Data point value of the emitted traces.span.metrics.calls metric should be 1 after each sent span

Actual Result

Data point value of the emitted traces.span.metrics.calls metric is 0 after each sent span

Collector version

v0.126.0

Environment information

No response

OpenTelemetry Collector configuration

receivers:
  otlp:
    protocols:
      grpc:
        endpoint: 0.0.0.0:4317
      http:
        endpoint: 0.0.0.0:4318

connectors:
  spanmetrics:
    exclude_dimensions: 
      - span.name
      - span.kind
      - status.code
    metrics_flush_interval: 10s
    aggregation_temporality: AGGREGATION_TEMPORALITY_DELTA
    
exporters:
  file:
    path: /tmp/spanmetrics.json
service:
  pipelines:
    traces:
      receivers: [otlp]
      exporters: [spanmetrics]
    metrics:
      receivers: [spanmetrics]
      exporters: [file]

Additional context

Proposed solution

I think we can check the aggregation type here so that we set the first value to 0 for cumulative metrics only. If my understanding is correct, the issue addressed by #39052 applies to cumulative metrics only.

[github-actions]

Pinging code owners:

• connector/spanmetrics: @portertech @Frapschen @iblancasa

See Adding Labels via Comments if you do not have permissions to add labels yourself.

[VihasMakwana]

Looks like a regression. Can you roll out a PR?

[jsonlsy]

Yep, I can create a PR for the proposed solution. Let me know if there are any other ideas/thoughts.