We have observed slowness in ITSI notable events and searches. In notable events we its taking time to complete the search and show the alert description. We checked o/s performance issues. CPU memory disk is normal.
It is always advisable to create knowledgebase search instead of adhoc search, adhoc search adds loads on performance.Notable Events Review displays notable events (alerts) generated by ITSI multi-KPI alerts, correlation searches, and anomaly detection algorithms. I would advise you to check the correlation searches as well, if searches are taking time to run then you will have to fine tune it.