ALTER SESSION SET EVENTS and ALTER SYSTEM SET EVENTS are undocumented in the Oracle9i and Oracle10g Oracle Database SQL Reference manuals as well as in Oracle Database SQL Language Reference 11g Release 1. The manual Oracle Database Performance Tuning Guide 10g Release 2 contains an ALTER SESSION statement for the presumably best known event 10046 at level 8. Yet, it is undocumented how to switch event 10046 off. The remaining levels of event 10046, which are also very useful, are undocumented too. Furthermore, there are hundreds of other undocumented events that may be set with ALTER SESSION and ALTER SYSTEM, some of which may be very useful too.
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