Blocked database session in an monitored Oracle database (4289745)

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Blocked database session in an monitored Oracle database
说明

An Oracle database encountered blocking sessions in the monitored database for about two hours. It appeared that the blocking may have been caused by the Foglight for Oracle database agent.
原因

In general, an Oracle reader never blocks other SQLs, i.e. a simple SELECT statement without "FOR UPDATE" clause will never block other SQL. All of the Foglight database agent collections are simple SELECT statements and would not create a lock in the database.
解决办法

From the "DBA_HIST_ACTIVE_SESS_HISTORY" all of the sessions were waiting on a "enq: TT - contention" wait event.
This is not a transaction/table lock, but rather an enqueue that is used to avoid deadlocks in parallel tablespace operations. The TT enqueue can be seen with parallel create tablespace and parallel point in time recovery (PITR).
It did not appear related to the Oracle agent SELECT statements. The recommendation was given to contact Oracle as there have been many Oracle bugs related to this wait event.

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产品：: Foglight
6.1.0, 6.0.0, 5.9.8, 5.9.7, 5.9.5, 5.9.4, 5.9.3, 5.9.2, 5.7.5, 5.7.1, 5.6.11, 5.6.10, 5.6.7, 5.6.5, 5.6.4, 5.6.3; Foglight for Databases
6.1.0, 6.0.0, 5.9.7, 5.9.5, 5.9.4, 5.9.3, 5.9.2

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