Slides from my performance talk at the 2023 Cassandra summit. Here I share my tools and process for improving Cassandra's performance. We look at the OODA loop, USE method, high level observability tools and system tools such as flame graphs and bcc-tools (ebpf). Using the example of giving more memory to Cassandra, we explore how to leverage async-profiler and bcc-tools to generate cpu flame graphs and histograms of I/O performance. We can see how identifying a performance bottleneck like time spent in decompression can guide us to solving the right problems - in this case resizing compression buffers.