Managing data center networks with low loss requires understanding traffic patterns, especially burstiness of the traffic, at fine time granularity. Yet, monitoring traffic with millisecond granularity fleet wide is challenging. To gain more visibility into our production network, we design millisampler, a BPF based lightweight traffic measurement tool deployed in every server in the entire fleet for continual monitoring that operates at high granularity timescale. Millisampler data allows us to characterize microbursts at millisecond or even microsecond granularity, and simultaneous data collection enables analysis of how synchronized bursts interact in rack buffers. We’ll discuss the design, implementation, and production experience with millisampler, and share some interesting observations we got with the millisampler data.