From Oracle documentation:
“Wait events are statistics that are incremented by a server process or thread to indicate that it had to wait for an event to complete before being able to continue processing.”
For example, wait events can be related to I/O, locks, memory allocation, etc.
The top events tell us what the server processes wait for the most. Eliminating these wait events will definately reduce execution time, since server processes will not have to wait this time for other operations to complete.
There are many wait event in Oracle databases, this is a list of some important and common wait events:
- buffer busy waits
- free buffer waits
- db file scattered read
- db file sequential read
- enqueue waits
- log buffer space
- log file sync
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