The short answer: insignificant. In real world scenarios, ESM does not negatively impact performance.
The long answer: because ESM only monitors selected processes, it uses considerably less resource than tools like top, prstat or Windows Task Manager. CPU consumption does however increase with the number of storage devices being monitored. Some real-world measurements for reference:
– on a 12-core system running a pair of Xeon X5650 processors, monitoring25 storage devices and 80 processes in real time, an ESM agent uses around 11% of one CPU thread (around 0.5% of overall system load)
– on a quad-core machine monitoring only 2 storage devices and 15 processes, an agent uses around 0.4% of one CPU thread (less than 0.1% of the overall system load)
ESM does not realistically impact system performance. Generally speaking SAS BI is a disk-bound platform and most environments ESM monitors have enough CPU headroom to allow it to run without impacting any other processes. Even though ESM tracks the logfiles written to disk by batch programs, these are read as they are written, meaning that they are generally accessed via the filesystem cache rather than the physical storage devices themselves.