Truncated gen ai tag values

[AlexandruRus23]

I've recently moved from using Semantic Kernel to MEAI.

I've noticed that ChatClient sets the chat history of a completion as an array on a tag gen_ai.input.messages while Semantic Kernel sets each message as an event on the span.

While both seem to be interpreted fine by the tools that I use, tag values usually have a limit on their length. This is usually configured by OTEL_ATTRIBUTE_VALUE_LENGTH_LIMIT. Going over that limit (which happens often for chat histories) leads to truncation and lost information.

Is there a way to configure one or the other or are there any plans to address this?

[stephentoub]

@TaoChenOSU, I may be reading it incorrectly, but it looks like SK is currently using a deprecated approach of adding an event for each message?

@TaoChenOSU / @JamesNK, assuming we're just talking about whether the complete chat history is stored in an attribute on the span or as an attribute on a event.gen_ai.client.inference.operation.details event, is there any reason to change from what we're currently doing?

@AlexandruRus23, my understanding is OTEL_ATTRIBUTE_VALUE_LENGTH_LIMIT is supposed to default to no limit. Are you explicitly setting a limit?

[JamesNK]

MEAI is just following the spec. I don't know what else it could do here.

A finite OTEL_ATTRIBUTE_VALUE_LENGTH_LIMIT and outputting large values aren't compatible. I assume people who decided on this approach to GenAI telemetry considered this situation 🤷

[AlexandruRus23]

I am setting OTEL_ATTRIBUTE_VALUE_LENGTH_LIMIT to 4095 atm.

Various APM providers have different limits over which (I think) they will get truncated:

NR: https://docs.newrelic.com/docs/opentelemetry/best-practices/opentelemetry-otlp/#attribute-limits (4095)
AppInsights: https://github.com/MicrosoftDocs/azure-monitor-docs/blob/main/articles/azure-monitor/app/includes/application-insights-limits.md (8,192)

I can look to remove the limit and use something that doesn't have a limit, but thought the problem how various standards and implementations meet each other is relevant.

The way of attaching an event to the span was circumventing this limitation. I didn't know it's being deprecated.