Randomly generated, unique identifier for a trace, set on all spans within it.

Encoded as 16 or 32 lowercase hex characters in big endian byte order, corresponding to 64 or 128 bits, For example, a 128bit trace ID looks like 4e441824ec2b6a44ffdc9bb9a6453df3

The logical operation this span represents in lowercase (e.g. rpc method). Set to empty string if unknown.

As these are lookup labels, take care to ensure names are low cardinality. For example, do not embed variables into the name.

The parent span ID or absent if this the root span in a trace.

Unique 64bit identifier for this operation within the trace.

Encoded as 16 lowercase hex characters. For example ffdc9bb9a6453df3

Epoch microseconds of the start of this span, possibly absent if incomplete.

For example, 1502787600000000 corresponds to 2017-08-15 09:00 UTC

This value should be set directly by instrumentation, using the most precise value possible. For example, gettimeofday or multiplying epoch millis by 1000.

There are three known edge-cases where this could be reported absent.

• A span was allocated but never started (ex not yet received a timestamp)
• The span's start event was lost
• Data about a completed span (ex tags) were sent after the fact

Duration in microseconds of the critical path, if known. Durations of less than one are rounded up. Duration of children can be longer than their parents due to asynchronous operations.

For example 150 milliseconds is 150000 microseconds.

True is a request to store this span even if it overrides sampling policy.

This is true when the X-B3-Flags header has a value of 1.