Oracle Wait Events

The occurrence of a wait event is not important.The *impact* of a wait event (or CPU) is what matters.

library cache: mutex X
=> related to concurrency. Processes compete for shared resources in the library cache, and to control who has access at any given point in time, we use mutexes, which are like lightweight latches, ie, structures to ensure that two people (processes) are not changing the same memory structure at the same time.

log file switch (checkpoint incomplete)
=> we wanted to reuse a redo log file but the underlying checkpoint to ensure all the database changes backed by that redo log was flushed to disk.

resmgr:cpu quantum
=> resource manager throttled back some process or processes because they were consuming excessive CPU.

We can't really deduce much without the full report, but typically, when we start seeing 'library cache: mutex X' and 'resmgr:cpu quantum' together, it often means the box is under CPU pressure, often from excessive parsing.

 

Library cache lock

This lock is also obtained as part of the operation to locate an object in the library cache (a library cache child latch is obtained to scan a list of handles, then the lock is placed on the handle once the object has been found).