The process waits for a latch that is currently busy (held by another process). Wait Time: The wait time increases exponentially and does not include spinning on the latch (active waiting). The maximum wait time also depends on the number of latches that the process is holding. There is an incremental wait of up to 2…
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…
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…
This event is used to wait for disk file operations (for example, open, close, seek, and resize). It is also used for miscellaneous I/O operations such as block dumps and password file accesses. Wait Time: The wait time is the actual time it takes to do the I/O Parameter Description FileOperation Type of file operation…
The session waits for the lock handle of a global lock request. The lock handle identifies a global lock. With this lock handle, other operations can be performed on this global lock (to identify the global lock in future operations such as conversions or release). The global lock is maintained by the DLM. Wait Time: The…
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…
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…
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…
A session waits on this event when it is requesting an exclusive mutex pin for a cursor object and it must wait because the resource is busy. The mutex pin for a cursor object can be busy either because a session is already holding it exclusive, or there are one or more sessions which are holding…
This wait is signaled while the control file’s shared information is written to disk. This is an atomic operation protected by an enqueue (CF), so that only one session at a time can write to the entire database. Wait Time: The wait time is the elapsed time of the write Parameter Description file# This identifies the…
Oracle Database Internal Mechanism 