Enqueue waits events usually causes problems in busy Oracle databases. But oracle online document only have some of them until 11gR2, not sure why. I paste these information here for quick reference.
In Oracle Database 10g Release 1, each enqueue type is represented by its own wait event, making it much easier to understand exactly what type of enqueue the session is waiting for. You do not need to decipher the values from the P1, P2, P3, P1RAW, P2RAW, and P3RAW columns in the V$SESSION_WAIT or the V$SESSION view.
The following table lists all the enqueue waits in Oracle Database 10g Release 1 and describes what the enqueue is for. This information is available in the X$KSQST structure. The aggregated statistics for each of these enqueue types is displayed by the view V$ENQUEUE_STAT.
| Enqueue Type | Description |
|---|---|
| enq: AD – allocate AU | Synchronizes accesses to a specific OSM (Oracle… |
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