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[EventSource] Clarify limitations of self-describing event format #45869

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Apr 22, 2025
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[EventSource] Clarify limitations of self-describing event format #45869

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[EventSource] Clarify limitations of self-describing event format
mdh1418 Apr 20, 2025
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Adjust EventAttribute metadata clarification
mdh1418 Apr 22, 2025
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2 changes: 1 addition & 1 deletion docs/fundamentals/runtime-libraries/system-diagnostics-tracing-eventsource.md
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Expand Up @@ -35,7 +35,7 @@ Historically, these two formats are derived from two formats that Event Tracing

The default event format is <xref:System.Diagnostics.Tracing.EventSourceSettings.EtwManifestEventFormat>, which is set if not specified on <xref:System.Diagnostics.Tracing.EventSourceSettings>. Manifest-based <xref:System.Diagnostics.Tracing.EventSource> objects generate an XML document representing the events defined on the class upon initialization. This requires the <xref:System.Diagnostics.Tracing.EventSource> to reflect over itself to generate the provider and event metadata.

To use self-describing (tracelogging) event format, construct your <xref:System.Diagnostics.Tracing.EventSource> using the <xref:System.Diagnostics.Tracing.EventSource.%23ctor(System.String)> constructor, the <xref:System.Diagnostics.Tracing.EventSource.%23ctor(System.String,System.Diagnostics.Tracing.EventSourceSettings)> constructor, or by setting the `EtwSelfDescribingEventFormat` flag on <xref:System.Diagnostics.Tracing.EventSourceSettings>. Self-describing sources generate minimal provider metadata on initialization and only generate event metadata when <xref:System.Diagnostics.Tracing.EventSource.Write(System.String)> is called.
To use self-describing (tracelogging) event format, construct your <xref:System.Diagnostics.Tracing.EventSource> using the <xref:System.Diagnostics.Tracing.EventSource.%23ctor(System.String)> constructor, the <xref:System.Diagnostics.Tracing.EventSource.%23ctor(System.String,System.Diagnostics.Tracing.EventSourceSettings)> constructor, or by setting the `EtwSelfDescribingEventFormat` flag on <xref:System.Diagnostics.Tracing.EventSourceSettings>. Self-describing sources generate minimal provider metadata on initialization and only generate event metadata when <xref:System.Diagnostics.Tracing.EventSource.Write(System.String)> is called. Unlike the manifest-based format, when listening via ETW only the Level, Keyword, and Opcode metadata are included from the <xref:System.Diagnostics.Tracing.EventAttribute> attribute. Other properties such as EventId or Message are not included.

In practice, these event format settings only affect usage with readers based on Event Tracing for Windows (ETW). They can, however, have a small effect on initialization time and per-event write times due to the time required for reflection and generating the metadata.

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