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# Trace
This package provides an interface for recording the latency of operations and logging details
about all operations where the latency exceeds a limit.
## Usage
To create a trace:
```go
func doSomething() {
opTrace := trace.New("operation", Field{Key: "fieldKey1", Value: "fieldValue1"})
defer opTrace.LogIfLong(100 * time.Millisecond)
// do something
}
```
To split an trace into multiple steps:
```go
func doSomething() {
opTrace := trace.New("operation")
defer opTrace.LogIfLong(100 * time.Millisecond)
// do step 1
opTrace.Step("step1", Field{Key: "stepFieldKey1", Value: "stepFieldValue1"})
// do step 2
opTrace.Step("step2")
}
```
To nest traces:
```go
func doSomething() {
rootTrace := trace.New("rootOperation")
defer rootTrace.LogIfLong(100 * time.Millisecond)
func() {
nestedTrace := rootTrace.Nest("nested", Field{Key: "nestedFieldKey1", Value: "nestedFieldValue1"})
defer nestedTrace.LogIfLong(50 * time.Millisecond)
// do nested operation
}()
}
```
Traces can also be logged unconditionally or introspected:
```go
opTrace.TotalTime() // Duration since the Trace was created
opTrace.Log() // unconditionally log the trace
```
### Using context.Context to nest traces
`context.Context` can be used to manage nested traces. Create traces by calling `trace.GetTraceFromContext(ctx).Nest`.
This is safe even if there is no parent trace already in the context because `(*(Trace)nil).Nest()` returns
a top level trace.
```go
func doSomething(ctx context.Context) {
opTrace := trace.FromContext(ctx).Nest("operation") // create a trace, possibly nested
ctx = trace.ContextWithTrace(ctx, opTrace) // make this trace the parent trace of the context
defer opTrace.LogIfLong(50 * time.Millisecond)
doSomethingElse(ctx)
}
```
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