Oracle – Active Sessions Waiting for Scheduler

High Log File Sync wait events mean that throughput on writing to the online redo logs is not high enough. This blog gives a great explanation of how to diagnose and troubleshoot that event:

http://logicalread.solarwinds.com/oracle-log-file-sync-wait-event-dr01/#.V_TSTvkrKUk

GC Busy and other GC wait events indicate RAC cluster related waits. We'd need to see a lot more detail to troubleshoot this accurately. That said, if you are having Log File Sync waits on some or all nodes, most likely the other nodes will start showing GC wait events. The nodes have to cooperate with each other. When one node has problems, the whole cluster is affected.

We opened a support ticket with Microsoft and they gave us a tool to run to gather metrics when issue was in progress. I couldn't run the tool during business hours since I didn't want it cause problems for working processes. Then in the evening, update statistics job ran for almost twice long than before. Probably that produced better query plans for queries running on next morning i.e. on Tuesday. It was way better than Monday. I observed the performance today. It's back to normal. I didn't have to use Microsoft tool at all. Go figure! Thank you.