What feature allows visualization of resource loading in RUM?

The feature that enables the visualization of resource loading in Real User Monitoring (RUM) is the waterfall chart. This tool provides a detailed breakdown of how various resources (like images, scripts, and stylesheets) are loaded over time. It visualizes each resource's loading duration, sequence, and the time taken to fully load, giving users a clear understanding of performance bottlenecks.

In a waterfall chart, the y-axis typically represents the resource name, while the x-axis indicates the time. Each bar in the chart shows the time taken for a specific resource to load, making it easier to identify which resources delay page rendering. By analyzing the waterfall chart, teams can pinpoint issues in resource loading, allowing them to optimize performance effectively.

Other features like APM tracing are focused on monitoring and optimizing back-end performance rather than frontend resource loading. Similarly, heat maps offer a visual representation of user interactions on a webpage but do not specifically track resource loading. Network request analysis provides insights into the overall network traffic but does not visualize loading in a time-based manner like the waterfall chart does. Thus, for a clear and effective visualization of resource loading, the waterfall chart is essential.