One of the most urgent challenges in event based performance analysis is the enormous amount of collected data. A real-time event reduction is crucial to enable a complete in-memory event tracing workflow, which circumvents the limitations of current parallel file systems to support event tracing on large scale systems. However, a traditional single flat memory buffer fails to support real-time event reduction. To address this issue, we present a hierarchical memory buffer, which is capable to support event reduction. We show that this hierarchical memory buffer does not introduce additional overhead, regardless of the grade of reduction. In addition, we evaluate its main parameter: the size of the internal memory bins. The hierarchical memory buffer is based on the Open Trace Format 2, a state-of-the-art Open Source event trace library used by the performance analysis tools VAMPIR, SCALASCA, and TAU.