public Trace setLevel(int level) {
        this.level = Math.min(Math.max(level, 0), 9);
        return this;
    }
Set the trace level. 0 means no tracing, 9 means enable all tracing.

@param level The level to set.
@return This, to allow chaining.
messagebus/src/main/java/com/yahoo/messagebus/Trace.java