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tracestate-handling.md

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TraceState Handling

Status: Development

In alignment to the TraceContext specification, this section uses the Augmented Backus-Naur Form (ABNF) notation of RFC5234, including the DIGIT rule in that document.

When setting TraceState values that are part of the OTel ecosystem, they MUST all be contained in a single entry using the ot key, with the value being a semicolon separated list of key-value pairs such as:

  • ot=p:8;r:62
  • ot=foo:bar;k1:13

The TraceContext specification defines support for multiple "tenants" each to use their own tracestate entry by prefixing tenant@ to tenant-specific values in a mixed tracing environment. OpenTelemetry recognizes this syntax but does not specify an interpretation for multi-tenant tracestate. The list can be formally defined as:

list        = list-member *( ";" list-member )
list-member = key ":" value

The complete list length MUST NOT exceed 256 characters, as defined by the TraceState value section, and the used keys MUST be unique.

Instrumentation libraries and clients MUST NOT use this entry, and they MUST instead use their own entry.

Key

The key is an identifier that describes an OTel concern. Simple examples are p, ts, or s1.

The key can be formally defined as:

key        = lcalpha *(lcalpha / DIGIT )
lcalpha    = %x61-7A ; a-z

Specific keys used by OTel concerns MUST be defined as part of the Specification, and hence it is forbidden to use any key that has not been defined in the Specification itself.

Value

The value is an opaque string. Although it has no maximum allowed length, it is recommended to use short values, as the entire list of key-values MUST NOT exceed 256 characters.

The value can be formally defined as:

value      = *(chr)
chr        = ucalpha / lcalpha / DIGIT / "." / "_" / "-"
ucalpha    = %x41-5A ; A-Z
lcalpha    = %x61-7A ; a-z

Setting values

Set values MUST be either updated or added to the ot entry in TraceState, in order to preserve existing values belonging to other OTel concerns. For example, if a given concern K wants to set k1:13:

  • ot=p:8;r:62 will become ot=p:8;r:62;k1:13.
  • ot=p:8;k1:7;r:62 will become ot=p:8;r:62;k1:13. Preserving the order is not required.

If setting a value ends up making the entire ot entry exceed the 256 characters limit, SDKs are advised to abort the operation and signal the user about the error, e.g.

traceState, ok := SetTraceStateValue(traceState, value)
if ok {
  // Successfully set the specified value, traceState was updated.
} else {
  // traceState was not updated.
}