摘要：Brendan Gregg, Oracle When I/O latency is presented as a visual heat map, some intriguing and beautiful patterns can emerge. These patterns provide insight into how a system is actually performing and what kinds of latency end-user applications experience. Many characteristics seen in these patterns are still not understood, but so far their analysis is revealing systemic behaviors that were previously unknown. Introduction to Latency Latency is time spent waiting. It has a direct impact on performance when induced by a synchronous component of an application request. This makes interpretation straightforward—the higher the latency, the worse the performance. Such a simple interpretation is not possible for many other statistics types that are commonly examined for performance analysis, such as utilization, IOPS (I/O per second), and throughput. Those statistics are often better suited for capacity planning and for understanding the nature of workloads. For identifying performance issues, however, understanding latency is essential.
