Is it ok to use tracer struct to pass data between TraceQueryStart and TraceQueryEnd?

[S-YOU]

type Tracer struct{
    startTime time.Time
}

func (t *Tracer) TraceQueryStart(...) {
  t.startTime = time.Now()
}

func (t *Tracer) TraceQueryEnd(...) {
   // log time taken by query
}

Is it safe to use?

[jackc]

Only if one Tracer is only ever used by one Conn at a time.

See the tracelog package for a concurrency-safe example of tracking query time.