Wait Event – read by other session

This event occurs when a session requests a buffer that is currently being read into the buffer cache by another session. Prior to release 10.1, waits for this event were grouped with the other reasons for waiting for buffers under the ‘buffer busy waits’ event. Wait Time: Time waited for the buffer to be read by the…

Wait Event – rdbms ipc message

The background processes (LGWR, DBWR, LMS0) use this event to indicate that they are idle and are waiting for the foreground processes to send them an IPC message to do some work. Wait Time: Up to 3 seconds. The parameter timeout shows the true sleep time.   Parameter Description timeout The amount of time that the session waits…

Wait Event – index block split

While trying to find an index key in an index block, Oracle noticed that the index block was being split. Oracle will wait for the split to finish and try to find the key again. Wait Time: The session will yield the CPU, so there is no actual waiting time   Parameter Description rootdba The root…

Wait Event – free buffer waits

This wait event can occur for several reasons. All buffer gets have been suspended. This could happen when a file was read-only and is now read/write. All the existing buffers must be invalidated since they are not linked to lock elements (needed when mounted parallel (shared)). So cache buffers are not assigned to data block…

Wait Event – enq: TX – row lock contention

This wait event can occur for several reasons. If one user is wanting to update or delete a row or rows that another session is modifying. The session holding the lock will release it when it performs a COMMIT or ROLLBACK. If a session is waiting due to potential duplicates in a UNIQUE index. If…

Wait Event – DFS db file lock

This event occurs only for the DBWR in Real Application Clusters. Each DBWR of every instance holds a global lock on each file in shared mode. The instance that is trying to offline the file will escalate the global lock from shared to exclusive. This signals the other instances to synchronize their SGAs with the…

Wait Event – db file single write

This event is used to wait for the writing of the file headers. Wait Time: The wait time is the actual time it takes to do the I/O   Parameter Description file# See “file#” block# See “block#” blocks This is the number of blocks that the session is trying to write in file# starting at block#

Wait Event – db file parallel write

This event occurs in the DBWR. It indicates the time that DBWR spends waiting for I/O completion. If asynchronous I/O is available, then the db file asynch I/O submit wait event captures any time spent in submitting I/Os to the underlying storage. When asynchronous I/O is not available, db file parallel write captures the time…

Wait Event – db file parallel read

This happens during recovery. It can also happen during buffer prefetching, as an optimization (rather than performing multiple single-block reads). Database blocks that must be changed as part of recovery are read in parallel from the database. Wait Time: Wait until all of the I/Os are completed   Parameter Description files This indicates the number of files…