Sampling overrides do not work for stacktrace attribute (at least in log4j2)

[morngaraf]

Expected behavior

Sampling overrides should work for stacktrace attribute applicationinsights.internal.log_error_stack.

Actual behavior

It does not work, pattern matcher is never executed with the provided regexp.

To Reproduce

Steps to reproduce the behavior:

1. Set the following sampling overrides in applicationinsights.json:

  "sampling": {
    "percentage": 100
  },
  "preview": {
    "sampling": {
      "overrides": [
        {
          "attributes": [
            {
              "key": "applicationinsights.internal.log_error_stack",
              "value": "<some valid regexp>",
              "matchType": "regexp"
            }
          ],
          "percentage": 0
        },
        {
          "attributes": [
            {
              "key": "applicationinsights.internal.logger_name",
              "value": "<some other valid regexp, which never matches a value in this attribute>",
              "matchType": "regexp"
            }
          ],
          "percentage": 0
        }
      ]
    }
  }

2. Let the app log some exception, e.g. logger.error("this is an error with some stacktrace", new IllegalArgumentException("exception message"));
3. Check logs / fiddler / appinsights, exception has been sent, though sampling is 0. The other option is to set a breakpoint in Pattern.matcher() with condition on pattern: it is hit for logger_name, but not for log_error_stack.

System information

• SDK Version: agent 3.2.3, Java 17
• OS type and version: Windows 10 x64, 21H1, 19043.1348
• Using spring-boot? - yes, 2.5.6
• Additional relevant libraries (with version, if applicable): configured spring-boot to use log4j2 instead of default logback (probably irrelevant, though I didn't try with default)

Logs

2021-11-24 01:01:34.630+03:00 DEBUG c.m.a.a.internal.exporter.Exporter - exporting span: SpanDataImpl{}, name=this is an error with some stacktrace, kind=INTERNAL, startEpochNanos=1637704894632635000, attributes={applicationinsights.internal.log=true, applicationinsights.internal.log_error_stack="java.lang.IllegalArgumentException: exception message
at ...
at java.base/java.lang.Thread.run(Thread.java:833)
", applicationinsights.internal.log_level="ERROR", applicationinsights.internal.logger_name="MyLoggerName", applicationinsights.internal.operation_name="GET /sample-check", thread.id=68}, events=[], links=[], status=ImmutableStatusData{statusCode=UNSET, description=}, endEpochNanos=1637704894632837500, hasEnded=true, totalRecordedEvents=0, totalRecordedLinks=0, totalAttributeCount=8}

Notes

I'm guessing that stacktrace attribute might be added later than sampling check, because it (attribute) does not seem to exist in the debugger:

but it is there in the logs. Not sure if this should be in feature request category.