excerpt from troubleshooting guide, credit to Sergio:
Harvest duration spikes:
a) If harvest duration is high all the time (> 7,500), the EM is overloaded, you need to review the hardware capacity and reduce the # of metrics and calculators.
b) If harvest duration spikes regularly at 5-min interval, it’s related to a volume polling thread which runs every 5 minute to get the disk/dir/file size of data, data/archive, traces.db, log file, and baselines.db set introscope.enterprisemanager.supportability.volumespace.enable=false.
c) If harvest duration spikes regulary at 1-hour interval and SPM is enabled, you need to disable SOA Deviation: set com.wily.introscope.soa.deviation.enable=false
Other possible symptoms: Your created calculators will start reporting zero hourly.
d) If harvest duration spikes at the same time GC duration also spikes: this might be due to a lack of memory: check heap size is enough, huge query or large amount of queries are happening, too many traces.