Copyright 2017, OpenCensus Authors Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
Package trace contains support for OpenCensus distributed tracing.
The following assumes a basic familiarity with OpenCensus concepts.See http:opencensus.io
Exporting Traces
To export collected tracing data, register at least one exporter. You can useone of the provided exporters or write your own.
trace.RegisterExporter(exporter)
By default, traces will be sampled relatively rarely. To change the samplingfrequency for your entire program, call ApplyConfig. Use a ProbabilitySamplerto sample a subset of traces, or use AlwaysSample to collect a trace on every run:
trace.ApplyConfig(trace.Config{DefaultSampler: trace.AlwaysSample()})
Be careful about using trace.AlwaysSample in a production application withsignificant traffic: a new trace will be started and exported for every request.
Adding Spans to a Trace
A trace consists of a tree of spans. In Go, the current span is carried in acontext.Context.
It is common to want to capture all the activity of a function call in a span. Forthis to work, the function must take a context.Context as a parameter. Add these twolines to the top of the function:
ctx, span := trace.StartSpan(ctx, "example.com/Run") defer span.End()
StartSpan will create a new top-level span if the contextdoesn't contain another span, otherwise it will create a child span.