public DebuggingSpan createSpan(String operation) {
        DebuggingSpan span = new DebuggingSpan(spanIdGenerator++, operation);
        if (debug) {
            span.setStartTime(System.nanoTime());
            DebuggingSpan parentSpan = spanStack.isEmpty() ? null : spanStack.peek();
            if (parentSpan != null) {
                span.setParentSpanId(parentSpan.getSpanId());
            } else {
                span.setParentSpanId(-1);
            }
            spanStack.push(span);
            execTrace.addSpan(span);
        }
        return span;
    }
Create a new span for OAP internal debugging trace and start.
@param operation operation
@return DebuggingSpan
oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/query/type/debugging/DebuggingTraceContext.java