We propose a new high resolution – temporal and spatial – 10 Gbps Ethernet monitoring technique based on time-coherent congestion ‘heatmaps’, revealing (all) the queue occupancies at μs granularity. Notably, queues are sampled with a slightly modified version of the new commodity Ethernet hardware congestion management protocol, i.e., IEEE 802 Quantized Congestion Notification. Our technique is evaluated through high-accuracy Layer-2 simulations of a 10 Gbps datacenter Ethernet fabric. Early results reveal that our proposal enables the detection of ephemeral – yet consequential – events and transients essential for datacenter workload characterization: e.g., TCP Incast, Head-of-Line blocking and congestion trees, which may trigger within 10s of μs and were not directly detectable until now.