Waits

The Waits window shows information about the Waits activity. 

It is splitted in two parts:

1. Waits ms/s chart

This shows the amount of time (in milliseconds) that sessions have spent waiting on various events per second. 
Event wait categories are aggregated into 8 categories:

Db file Occurs when a session issues an I/O request against an Oracle datafile.
(db file parallel write + db file scattered read + db file sequential read + db file single write)
Log file sync/write When a COMMIT is issued, the redo log writer flushed the content of the redo log to the redo file. The session waits for the write to complete to return control.
(log file parallel write + log file sync)
Log file space/switch Occurs when there is not enough free space in the  redo log buffer to make a redo log entry.
(log buffer space + log file switch completion)
Buffer busy Occurs when a session tries to access a block currently used by another session.
Latch free Occurs when a session tries to acquire a latch currently held by another session.
Enqueue Occurs when a session waits to obtain a lock.
Direct path I/O During Direct Path operations the data is asynchronously written to the database files. At some stage the session needs to make sure that all outstanding asynchronous I/O have been completed to disk. 
(direct path read + direct path write)
Control file I/O Occurs when a session accesses the control file. 
(control file parallel write + control file sequential read)

 

2. Waits per event

The grid located at the top shows each individual wait event with the total number of waits, the time waited and the average waited time.

By default, the last snapshot is displayed in the grid. Use the slidder (or the arrow buttons) located at the top of the grid to navigate through the collected snapshots. In monitoring, the "Update" button must be unchecked to be able to navigate through the collected snapshots.

Select a wait event in the grid (radio button at the left of the grid) to update the two graphes located at the bottom of the window.

Time waited (ms/s)

Amount of time (in milliseconds) that sessions have spent waiting on the selected event per second since the last snapshot.

Waits/s

Number of waits per second since the last snapshot.

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